Image forming apparatus

Abstract

To appropriately adjust a transfer voltage to an image preferred by a user.SOLUTION: An image forming apparatus has: an image carrier 44b; transfer means 45b; application means 76; an output mode execution unit 31d that outputs a chart 100; a density information acquisition unit 3 that is related to density of a test image on a recording material; a setting unit 30 that sets a transfer voltage on the basis of the density information; and an input unit 70 that receives input of instruction information. The execution unit 31d can control to transfer a plurality of first test images with first density on the recording material S, and can control to transfer a plurality of second test images with second density higher than the first density to the recording material S. According to the instruction information input to the input unit 70, the setting unit 30 can set a first transfer voltage by using at least the information on the density of the first test images (priority to half tone), or can set a second transfer voltage by using at least the information on the density of the second test images without using the information on the density of the first test images (priority to solid image).SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] This invention relates to image forming apparatus such as photocopiers, printers, and facsimile machines that use electrophotographic or electrostatic recording methods. [Background technology]

[0002] In image forming apparatuses using electrophotography or similar methods, a toner image formed on an image carrier such as a photoreceptor or intermediate transfer body is transferred to a recording material. The transfer of the toner image from the image carrier to the recording material is often performed by applying a transfer voltage to a transfer member, such as a transfer roller, which contacts the image carrier to form a transfer area. The transfer voltage can be determined based on a transfer portion voltage corresponding to the electrical resistance of the transfer area detected during a pre-rotation process before image formation, and a recording material portion voltage corresponding to a preset type of recording material. This allows for setting an appropriate transfer voltage according to environmental fluctuations, the usage history of the transfer member, and the type of recording material.

[0003] However, because the types and conditions of recording materials used in image formation vary, the default recording material distribution voltage set in advance may result in an excess or deficiency in the transfer voltage. Therefore, it has been proposed to provide an adjustment mode that adjusts the set transfer voltage according to the recording material actually used in image formation.

[0004] Patent Document 1 proposes an image forming apparatus capable of performing an adjustment mode to adjust the setting voltage of the secondary transfer voltage. In this adjustment mode, a chart is output on a single recording material in which multiple patches (test images) are transferred, with the secondary transfer voltage switched for each patch. The density of each patch is then detected, and the optimal secondary transfer voltage conditions are selected according to the detection results. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2013-37185 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, with conventional adjustment modes, users were sometimes unable to select the optimal adjustment value for the image they actually wanted to output, for example, when using recording materials with difficult transfer properties (where it is difficult to set transfer conditions that yield good transfer). Generally, the higher the density of the toner image to be transferred, the larger the absolute value of the transfer voltage required. However, when using recording materials with difficult transfer properties, for example, it can be difficult to transfer from midtones to solid colors well with a single transfer voltage.

[0007] Therefore, the objective of the present invention is to enable users to appropriately adjust the transfer voltage for images they prefer. [Means for solving the problem]

[0008] The above objective is achieved by the image forming apparatus according to the present invention. In summary, the present invention comprises an image carrier that carries a toner image, a transfer device that transfers the toner image from the image carrier to a recording material, an application unit that applies a voltage to the transfer device, a detection unit that detects density information relating to the density of the image on the recording material onto which the image is transferred by the transfer device, a control unit that performs a setting mode operation to transfer a plurality of test images onto the recording material by applying a plurality of different test voltages to the transfer device when not forming an image, and set the transfer voltage to be applied to the transfer device when forming an image based on the detection result detected by the detection unit of the test images transferred onto the recording material, and a reception unit that receives instruction information, wherein when the setting mode operation is performed to set the transfer voltage in a one-sided mode in which an image is formed on one side of a predetermined recording material, The input receiving unit is capable of receiving instruction information that selectively specifies a mode to be executed from among a plurality of modes, including a first setting mode in which the transfer voltage set in the setting mode satisfies a first predetermined condition, and a second setting mode in which the transfer voltage set in the setting mode satisfies a second predetermined condition different from the first predetermined condition, wherein the test image includes a plurality of first test images having a first density on the recording material and a plurality of second test images having a second density on the recording material, wherein the second density is higher than the first density, the first predetermined condition includes a first condition relating to the plurality of first test images, the second predetermined condition includes a second condition relating to the plurality of first test images, and the second condition is different from the first condition. In the first setting mode, the transfer voltage is set prioritizing the transferability of an image with a first predetermined density, and in the second setting mode, the transfer voltage is set prioritizing the transferability of an image with a second predetermined density that is higher than the first predetermined density. This is an image forming apparatus characterized by the following features. [Effects of the Invention]

[0009] According to the present invention, the user can appropriately adjust the transfer voltage for the image they prioritize. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic cross-section of an image forming apparatus. [Figure 2] This is a schematic block diagram of the control system of an image forming apparatus. [Figure 3] It is a flowchart showing an outline of the procedure for secondary transfer voltage control. [Figure 4] It is a graph showing an example of voltage-current characteristics obtained by secondary transfer voltage control. [Figure 5] It is a table showing an example of a recording material sharing voltage table. [Figure 6] It is a schematic diagram of a chart output in adjustment mode. [Figure 7] It is a schematic diagram of a chart output in adjustment mode. [Figure 8] It is a flowchart showing an outline of the procedure for the adjustment mode in Example 1. [Figure 9] It is a schematic diagram of a paper type category selection screen. [Figure 10] It is a schematic diagram of a paper feeding unit selection screen. [Figure 11] It is a schematic diagram of a secondary transfer voltage adjustment screen in Example 1. [Figure 12] It is a graph showing the transition of the secondary transfer voltage at the time of chart output. [Figure 13(a)] It is a table showing an example of the relationship between the patch number and the adjustment value of the chart. [Figure 13(b)] It is a table showing an example of the relationship between the patch number and the adjustment value of the chart. [Figure 13(c)] It is a table showing an example of the relationship between the patch number and the adjustment value of the chart. [Figure 14] It is a graph showing the transition of the secondary transfer voltage at the time of chart output. [Figure 15] It is a schematic diagram for explaining a method of detecting the position of a trigger patch. [Figure 16] It is a graph for explaining the intermediate tone priority mode in Example 1. [Figure 17] It is a graph for explaining the solid image priority mode in Example 1. [Figure 18] It is a flowchart showing an outline of the procedure for the adjustment mode in Example 2. [Figure 19]This is a schematic diagram of the secondary transfer voltage adjustment screen in Example 2. [Figure 20] This graph illustrates the low-concentration midtone-priority mode in Example 2. [Figure 21] This graph illustrates the high-concentration midtone-priority mode in Example 2. [Figure 22] This is a graph illustrating the solid image priority mode in Example 2. [Figure 23] This is a flowchart illustrating the general procedure for the adjustment mode in Example 3. [Figure 24] This is a schematic diagram of the secondary transfer voltage adjustment screen in Example 3. [Figure 25] This is a graph illustrating the low-concentration priority mode in Example 3. [Figure 26] This is a graph illustrating the high-concentration priority mode in Example 3. [Modes for carrying out the invention]

[0011] The image forming apparatus according to the present invention will be described in more detail below with reference to the drawings.

[0012] [Example 1] 1. Configuration of the image forming apparatus Figure 1 is a schematic cross-sectional view of the image forming apparatus (image forming system) 1 of this embodiment. In this embodiment, the image forming apparatus 1 is configured by combining a printer unit 2 that performs image formation and a sensing unit 3 that reads a chart to adjust the secondary transfer voltage. In this embodiment, the printer unit 2 is configured as a tandem-type full-color printer employing an intermediate transfer method that is capable of forming a full-color image on the recording material S using an electrophotographic method. Although the recording material S is sometimes referred to as "paper," as will be described later, the recording material S is not limited to paper.

[0013] The printer unit 2 includes a paper feeding unit 4, an image forming unit 5, a control unit 30, a data transfer unit 6 to the sensing unit 3, an operation unit 70, an image reading unit 80, and the like. In Figure 1, only one paper feeding unit 4 is shown, but the printer unit 2 may have multiple paper feeding units 4. Inside the main body 10 of the image forming apparatus 1 (printer unit 2), there is a temperature sensor 71 (Figure 2) capable of detecting the internal temperature of the main body 10 (internal temperature), and a humidity sensor 72 (Figure 2) capable of detecting the internal humidity of the main body 10 (internal humidity). The temperature sensor 71 and humidity sensor 72 are examples of environmental detection means for detecting environmental information, which is at least one of the temperature or humidity inside or outside the image forming apparatus 1, respectively. The printer unit 2 can form a four-color full-color image on a recording material (sheet, transfer material) S based on image information (image signal) from the image reading unit 80 or an external device 200 (Figure 2). External devices 200 include host devices such as personal computers, or digital cameras and smartphones. The recording material S is on which a toner image is formed, and specific examples include paper such as plain paper and cardboard, as well as paper substitutes such as synthetic resin sheets (synthetic paper) and overhead projector sheets.

[0014] The image forming unit 5 is capable of forming an image based on image information on recording material S that is fed from the paper feeding unit 4 and moves along the transport path P. The image forming unit 5 has a plurality of image forming units, namely the first, second, third, and fourth image forming units 50y, 50m, 50c, and 50k, which each form images of yellow (Y), magenta (M), cyan (C), and black (Bk), respectively. The image forming unit 5 also has an intermediate transfer unit 44, a secondary transfer device 45, a fixing device 46, and the like. Elements with the same or corresponding functions or configurations in each image forming unit 50y, 50m, 50c, and 50k may be described collectively by omitting the suffixes y, m, c, and k that indicate that they are elements for one of the colors Y, M, C, and Bk.

[0015] The image forming unit 50 has a photosensitive drum 51, which is a rotatable drum-type (cylindrical) photoreceptor (electrophotographic photoreceptor) as a first image carrier. The image forming unit 50 also has a charging roller 52, which is a roller-type charging member as a charging means. The image forming unit 50 also has an exposure device 42 as an exposure means. The image forming unit 50 also has a developing device 20 as a developing means. The image forming unit 50 also has a primary transfer roller 47, which is a roller-type primary transfer member as a primary transfer means (the primary transfer roller 47 also constitutes the intermediate transfer unit 44). The image forming unit 50 also has a pre-exposure device 54 as a static elimination means. The image forming unit 50 also has a drum cleaning device 55 as a photoreceptor cleaning means. The image forming unit 50 also has a toner bottle 41 as a developer supply container. The image forming unit 50 forms a toner image on the intermediate transfer belt 44b, which will be described later.

[0016] The photosensitive drum 51 is movable (rotatable) and carries an electrostatic image (electrostatic latent image) or toner image. In this embodiment, the photosensitive drum 51 is a negatively charged organic photoreceptor (OPC) with an outer diameter of 30 mm. The photosensitive drum 51 has an aluminum cylinder as a substrate and a surface layer formed on its surface. In this embodiment, the surface layer has three layers, which are coated and laminated on the substrate in the following order: an undercoat layer, a photocharge generation layer, and a charge transport layer. When the image forming operation is started, the photosensitive drum 51 is rotated by a motor (not shown) as a driving means at a predetermined peripheral speed (process speed) in the direction of arrow R1 (counterclockwise direction) in Figure 1.

[0017] The surface of the rotating photosensitive drum 51 is uniformly charged to a predetermined potential of a predetermined polarity (negative polarity in this embodiment) by the charging roller 52. In this embodiment, the charging roller 52 is a rubber roller positioned in contact with the surface of the photosensitive drum 51. The charging roller 52 rotates in conjunction with the rotation of the photosensitive drum 51. A charging power supply 73 (Figure 2), which serves as a means for applying a charging voltage (charging voltage application unit), is connected to the charging roller 52. During the charging process, the charging power supply 73 applies a predetermined charging voltage (charging bias) to the charging roller 52.

[0018] The surface of the charged photosensitive drum 51 is scanned and exposed by the exposure device 42 based on image information, and an electrostatic image is formed on the photosensitive drum 51. In this embodiment, the exposure device 42 is a laser scanner. The exposure device 42 emits laser light according to the separated color image information output from the control unit 30 and scans and exposes the surface (outer surface) of the photosensitive drum 51.

[0019] The electrostatic image formed on the photosensitive drum 51 is developed (visualized) by the developing device 20 when toner is supplied, and a toner image (toner image, developer image) is formed on the photosensitive drum 51. In this embodiment, the developing device 20 contains a two-component developer comprising non-magnetic toner particles (toner) and magnetic carrier particles (carrier) as the developer. Toner is supplied to the developing device 20 from the toner bottle 41. The developing device 20 has a developing sleeve 24 as a developer carrier (developing member). The developing sleeve 24 is made of a non-magnetic material such as aluminum or non-magnetic stainless steel (aluminum in this embodiment). A magnetic roller, which is a roller-shaped magnet, is fixedly positioned inside the developing sleeve 24 so as not to rotate relative to the main body (developing container) of the developing device 20. The developing sleeve 24 carries the developer and transports it to the developing area facing the photosensitive drum 51. A developing power supply 74 (Figure 2) is connected to the developing sleeve 24 as a developing voltage application means (developing voltage application unit). The developing power supply 74 applies a predetermined developing voltage (developing bias) to the developing sleeve 24 during the developing process. In this embodiment, toner charged with the same polarity as the charging polarity of the photosensitive drum 51 (negative polarity in this embodiment) adheres to the exposed area (image area) on the photosensitive drum 51, where the absolute value of the potential has decreased after uniform charging treatment and exposure (reverse developing method). In this embodiment, the normal charging polarity of the toner, which is the main charging polarity of the toner during development, is negative polarity.

[0020] An intermediate transfer belt 44b, which is an intermediate transfer body composed of an endless belt as a second image carrier, is positioned opposite the four photosensitive drums 51y, 51m, 51c, and 51k. The intermediate transfer belt 44b is wrapped around a plurality of tension rollers (support rollers), namely a drive roller 44a, a tension roller 44d, and a secondary transfer inner roller 45a, and is stretched under a predetermined tension. The intermediate transfer belt 44b is movable (rotatable) and carries the toner image. The drive roller 44a is rotationally driven by a motor (not shown) as a driving means, causing the intermediate transfer belt 44b to rotate (move around). The tension roller 44d controls the tension of the intermediate transfer belt 44b to be constant. The tension roller 44d is subjected to a force that pushes the intermediate transfer belt 44b from the inner circumferential surface side to the outer circumferential surface side by the biasing force of a spring (not shown) as a biasing means. This force applies a tension of approximately 2 to 5 kg in the circumferential direction (direction of surface movement) to the intermediate transfer belt 44b. The secondary transfer inner roller 45a also constitutes the secondary transfer apparatus 45, as will be described later. The intermediate transfer belt 44b is driven by the drive roller 44a and rotates (circumferentially moves) in the direction of arrow R2 (clockwise) in Figure 1 at a predetermined circumferential speed (process speed) corresponding to the circumferential speed of the photosensitive drum 51. On the inner circumferential surface side of the intermediate transfer belt 44b, primary transfer rollers 47y, 47m, 47c, and 47k are arranged, corresponding to the four photosensitive drums 51y, 51m, 51c, and 51k, respectively. In this embodiment, the primary transfer roller 47 is positioned opposite the photosensitive drum 1 via the intermediate transfer belt 44b and sandwiches the intermediate transfer belt 44b between itself and the photosensitive drum 51. As a result, the primary transfer roller 47 contacts the photosensitive drum 51 via the intermediate transfer belt 44b, forming a primary transfer section (primary transfer nip section) N1 where the photosensitive drum 51 and the intermediate transfer belt 44b are in contact. The tension rollers other than the drive roller 44a and each of the primary transfer rollers 47y, 47m, 47c, and 47k rotate in conjunction with the rotation of the intermediate transfer belt 44b. In addition, a belt cleaning device 60, which serves as an intermediate transfer body cleaning means, is positioned on the outer circumferential surface side of the intermediate transfer belt 44b, facing the drive roller 44a via the intermediate transfer belt 44b.The intermediate transfer unit 44 is composed of an intermediate transfer belt 44, tension rollers 44a, 44d, 45a, primary transfer rollers 47y, 47m, 47c, 47k, a belt cleaning device 60, and the like.

[0021] The toner image formed on the photosensitive drum 51 is first transferred in the primary transfer section N1 onto the rotating intermediate transfer belt 44b by the action of the primary transfer roller 47. A primary transfer power supply 75 (Figure 2), which serves as a primary transfer voltage application means (primary transfer voltage application unit), is connected to the primary transfer roller 47. During the primary transfer process, the primary transfer power supply 75 applies a predetermined primary transfer voltage (primary transfer bias), which is a DC voltage with the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner, to the primary transfer roller 47. A voltage detection sensor 75a, which serves as a voltage detection means (voltage detection unit) for detecting the output voltage, and a current detection sensor 75b, which serves as a current detection means (current detection unit) for detecting the output current, are connected to the primary transfer power supply 75 (Figure 2). In this embodiment, primary transfer power supplies 75y, 75m, 75c, and 75k are provided for each of the primary transfer rollers 47y, 47m, 47c, and 47k, respectively, and the primary transfer voltage applied to the primary transfer rollers 47y, 47m, 47c, and 47k can be individually controlled. In this embodiment, when a positive primary transfer voltage is applied to the primary transfer roller 47, the negative polarity toner image on the photosensitive drum 51 is primary transferred onto the intermediate transfer belt 44b. For example, when forming a full-color image, the toner images of each color, Y, M, C, and Bk, formed on each of the photosensitive drums 51y, 51m, 51c, and 51k are sequentially superimposed onto the intermediate transfer belt 44b in a multiple transfer process.

[0022] On the outer circumferential surface of the intermediate transfer belt 44b, a roller-type secondary transfer member, the secondary transfer outer roller 45b, is positioned opposite the secondary transfer inner roller 45a, which acts as an opposing member via the intermediate transfer belt 44b. The secondary transfer outer roller 45b, together with the secondary transfer inner roller 45a, constitutes the secondary transfer device 45 as a secondary transfer means. The secondary transfer outer roller 45b contacts the secondary transfer inner roller 45a via the intermediate transfer belt 44b, forming a secondary transfer section (secondary transfer nip section) N2 where the intermediate transfer belt 44b and the secondary transfer outer roller 45b are in contact. The toner image formed on the intermediate transfer belt 44b is secondarily transferred in the secondary transfer section N2 to the recording material S, which is held between the intermediate transfer belt 44b and the secondary transfer outer roller 45b and transported (passing through the secondary transfer section N2) by the action of the secondary transfer device 45. In this embodiment, a positive polarity secondary transfer voltage is applied to the secondary transfer outer roller 45b, thereby secondary transferring the negative polarity toner image on the intermediate transfer belt 44b onto the recording material S. The recording material S is fed from the paper feeding unit 4 in parallel with the toner image formation operation described above, and is transported to the secondary transfer unit N2 by the register roller 11, which is a transport member provided on the transport path P, in time with the toner image on the intermediate transfer belt 44b.

[0023] Thus, the secondary transfer device 45 is configured to include a secondary transfer inner roller 45a as an opposing member and a secondary transfer outer roller 45b as a secondary transfer member. A secondary transfer power supply 76 (Figure 2), which serves as a secondary transfer voltage application means (secondary transfer voltage application unit), is connected to the secondary transfer outer roller 45b. During the secondary transfer process, the secondary transfer power supply 76 applies a predetermined secondary transfer voltage to the secondary transfer outer roller 45b, which is a DC voltage with the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner. A voltage detection sensor 76a, which serves as a voltage detection means (voltage detection unit) for detecting the output voltage, and a current detection sensor 76b, which serves as a current detection means (current detection unit) for detecting the output current, are connected to the secondary transfer power supply 76 (Figure 2). In this embodiment, the core metal of the secondary transfer inner roller 45a is connected to ground potential. When the recording material S is supplied to the secondary transfer unit N2, a constant voltage controlled secondary transfer voltage with the opposite polarity to the normal charging polarity of the toner is applied to the secondary transfer outer roller 45b. In this embodiment, for example, a secondary transfer voltage of 1 to 6.5 kV is applied, and a current of about 15 to 100 μA is passed through, thereby secondary transferring the toner image on the intermediate transfer belt 44b onto the recording material S. In this embodiment, the secondary transfer inner roller 45a is connected to ground potential, and a voltage is applied to the secondary transfer outer roller 45b from the secondary transfer power supply 76. Alternatively, a voltage may be applied to the secondary transfer inner roller 45a, which is the secondary transfer member, from the secondary transfer power supply 76, and the secondary transfer outer roller 45b, which is the opposing member, may be connected to ground potential. In this case, a DC voltage with the same polarity as the normal charging polarity of the toner is applied to the secondary transfer inner roller 45a.

[0024] The recording material S onto which the toner image has been transferred is transported to a fixing device 46, which serves as a fixing means. The fixing device 46 includes a fixing roller 46a and a pressure roller 46b. The fixing roller 46a has a built-in heater as a heating means. The pressure roller 46b is pressed toward the fixing roller 46a, forming a fixing section (fixing nip section) N3 where the fixing roller 46a and the pressure roller 46b come into contact. The recording material S, which carries the unfixed toner image, is heated and pressurized in the fixing section N3 by being transported while sandwiched between the fixing roller 46a and the pressure roller 46b. As a result, the toner image is fixed (melted and solidified) onto the recording material S. The temperature of the fixing roller 46a (fixing temperature) is detected by a fixing temperature sensor 77 (Figure 2) and controlled by a control unit 30.

[0025] In the case of single-sided printing, where an image is formed on one side of the recording material S, the recording material S, on which the toner image has been fixed to one side as described above, is transferred directly from the transfer unit 6 to the sensing unit 3. On the other hand, in the case of double-sided printing, where an image is formed on both sides of the recording material S, the recording material S, on which the toner image has been fixed to the first side as described above, is transported to the inversion transport path 7 by an inversion transport roller 12 or the like, which acts as an inversion transport member. In the inversion transport path 7, the recording material S, on which the toner image has been fixed to the first side, is turned over and supplied again to the secondary transfer unit N2 by a double-sided transport roller 13 or the like, which acts as a double-sided transport member. The recording material S supplied again to the secondary transfer unit N2 in this way has the toner image transferred to the second side and fixed, and then is transferred from the transfer unit 6 to the sensing unit 3. In this way, the image forming apparatus 1 (printer unit 2) of this embodiment is capable of performing double-sided printing (automatic double-sided printing, double-sided printing), which forms an image on both sides of a single recording material S. The double-sided mechanism 14 is composed of the inversion transport path 7, the inversion transport roller 12, the double-sided transport roller 13, and the like. The recording material S on which the image has been formed passes through the inside of the sensing unit 3 and is discharged (output) to the discharge unit 8 located outside the sensing unit 3 (image forming apparatus 1). In the adjustment mode described later, when a chart formed by transferring patches to the recording material S is output, the patches on the chart are read as the recording material S passes through the inside of the sensing unit 3, and then the recording material S is discharged to the discharge unit 8.

[0026] After the primary transfer, the photosensitive drum 51 is electrostatically discharged from its surface by the pre-exposure device 54. Furthermore, toner remaining on the photosensitive drum 51 during the primary transfer process that was not transferred to the intermediate transfer belt 44b (primary transfer residue toner) is removed and recovered from the surface of the photosensitive drum 51 by the drum cleaning device 55. The drum cleaning device 55 has a cleaning blade as a cleaning member. The cleaning blade is a plate-shaped member that contacts the photosensitive drum 51 with a predetermined pressing force. The cleaning blade is in contact with the surface of the photosensitive drum 51 in a counter-direction with respect to the rotation direction of the photosensitive drum 51, such that the tip of its free end faces upstream in the rotation direction of the photosensitive drum 51. Additionally, toner remaining on the intermediate transfer belt 44b during the secondary transfer process that was not transferred to the recording material S (secondary transfer residue toner) and other adhering materials such as paper dust are removed and recovered from the surface of the intermediate transfer belt 44b by the belt cleaning device 60. In this embodiment, the belt cleaning device 60 is configured to have a cleaning blade similar to the drum cleaning device 55. The toner and other materials collected by the drum cleaning device 55 and the belt cleaning device 60 are transported to a collection container (not shown) and stored there.

[0027] Furthermore, the image forming apparatus 2 can also form single-color or multi-color images, such as a black single-color image, by using image forming units 50 for several of the desired single colors or four colors.

[0028] In this embodiment, the primary transfer roller 47 has an elastic layer of ion-conductive foamed rubber (NBR rubber) and a core metal. The outer diameter of the primary transfer roller 47 is, for example, 15 to 20 mm. Furthermore, the primary transfer roller 47 has an electrical resistance value of 1 × 10⁻¹⁰. 5 ~1 × 10 8 A roller with a value of Ω (N / N (measured at 23°C, 50%RH, with 2kV applied)) can be suitably used.

[0029] In this embodiment, the intermediate transfer belt 44b is an endless belt having a two-layer structure consisting of a base layer and a surface layer from the inner circumferential surface side. Suitable materials for the base layer include resins such as polyimide and polycarbonate, or various types of rubber containing an appropriate amount of carbon black as an antistatic agent. The thickness of the base layer is, for example, 0.05 to 0.15 mm. Suitable materials for the surface layer include resins such as fluororesin. The surface layer reduces the adhesion of toner to the surface of the intermediate transfer belt 44b, facilitating the transfer of toner to the recording material S in the secondary transfer section N2. The thickness of the surface layer is, for example, 0.0002 to 0.020 mm. Suitable materials for the surface layer include one type of resin material such as polyurethane, polyester, or epoxy resin, or two or more types of elastic materials such as elastic rubber, elastomer, or butyl rubber. Then, a surface layer can be formed on this substrate by dispersing one or more types of powders or particles, such as fluororesin, or particles with different particle sizes, as a material that reduces surface energy and enhances lubricity. In this embodiment, the intermediate transfer belt 44b has a volume resistivity of 5 × 10⁻⁶ 8 ~1 × 10 14 The friction coefficient is Ω·cm (23℃, 50%RH), and the static friction coefficient is 0.15~0.6 (23℃, 50%RH, HEIDON type 94i). In this embodiment, the intermediate transfer belt 44b has a two-layer structure, but it may also be a single-layer structure of the material corresponding to the base layer described above.

[0030] In this embodiment, the secondary transfer outer roller 45b has an elastic layer of ion-conductive foamed rubber (NBR rubber) and a core metal. The outer diameter of the secondary transfer outer roller 45b is, for example, 20 to 25 mm. The electrical resistance value of the secondary transfer outer roller 45b is 1 × 10⁻¹⁰. 5 ~1 × 10 8 A roller with a value of Ω (N / N (measured at 23°C, 50%RH, with 2kV applied)) can be suitably used.

[0031] Furthermore, in each image forming unit 50, the photosensitive drum 51 and at least one of the process means acting thereon—the charging roller 52, the developing device 20, and the drum cleaning device 55—may be integrated into a single process cartridge. This unit may be detachable from the main body 10 of the device.

[0032] Furthermore, an automatic document transport device 81 and an image reading unit 80 are arranged on the upper part of the main body 10 of the device. The automatic document transport device 81, as a document transport means, automatically transports a sheet such as recording material S on which an image (text or image) of the document is formed to the reading position of the image reading unit 80 (which may consist of at least a part of the platen glass 82 described later). The image reading unit 80, as a reading means, can read the image on the sheet transported to the reading position by the automatic document transport device 81. The image reading unit 80 can also read the image on a sheet such as recording material S on which an image (text or image) of the document is formed, which is placed on the platen glass 82. The image reading unit 80 is configured to illuminate the sheet with a light source (not shown) and read the image on the sheet with an image reading element (not shown) at a predetermined dot density. In other words, the image reading unit 80 optically reads the image on the sheet and converts it into an electrical signal.

[0033] 2. Control Modes Figure 2 is a block diagram illustrating the schematic configuration of the control system of the image forming apparatus 1 in this embodiment. As shown in Figure 2, the control unit 30 is composed of a computer. The control unit 30 includes, for example, a CPU 31, a ROM 32 (including a rewritable one) that stores programs for controlling each part, a RAM 33 that temporarily stores data, and an input / output circuit (I / F) 34 that inputs and outputs signals to and from the outside. The CPU 31 is a microprocessor that oversees the entire control of the image forming apparatus 1 and is the main component of the system controller. The CPU 31 is connected to the paper feeding unit 4, the image forming unit 5, the transfer unit 6, the operation unit 70, the sensing unit 3, and the image reading unit 80 via the input / output circuit 34, and exchanges signals with each of these units and controls the operation of each of these units. The ROM 32 stores image forming control sequences for forming images on the recording material S. For example, the control unit 30 is connected to a charging power supply 73, a developing power supply 74, a primary transfer power supply 75, and a secondary transfer power supply 76, each of which is controlled by signals from the control unit 30. Furthermore, the control unit 30 is connected to a temperature sensor 71, a humidity sensor 72, a voltage detection sensor 75a and a current detection sensor 75b of the primary transfer power supply 75, a voltage detection sensor 76a and a current detection sensor 76b of the secondary transfer power supply 76, and a fixing temperature sensor 77. Signals detected by each sensor are input to the control unit 30.

[0034] Operation section (Reception Department) The 70 has an operation button (such as a numeric keypad) as an input means and a display unit 70a consisting of a liquid crystal panel or the like as a display means. In this embodiment, the display unit 70a is configured as a touch panel and also functions as an input means. Operators such as users and service personnel can input instructions to the control unit 30 to execute a job (described later) by operating the operation unit 70. The control unit 30 can receive signals from the operation unit 70 and control the various devices of the image forming apparatus 1 to operate and execute the job. The image forming apparatus 1 can also execute jobs based on image forming signals (image data, control commands) from external devices 200 such as a personal computer.

[0035] In this embodiment, the control unit 30 includes an image formation preparation process unit 31a, an ATVC control process unit 31b, an image formation process unit 31c, and an adjustment process unit 31d. The control unit 30 also includes a primary transfer voltage storage / calculation unit 31e and a secondary transfer voltage storage / calculation unit 31f. These process units and storage / calculation units may be provided as part of the CPU 31 and ROM 32 / RAM 33. For example, the control unit 30 (more specifically the image formation process unit 31c) can be controlled to execute a job as described above. The control unit 30 (more specifically the ATVC control process unit 31b) can be controlled to execute ATVC control (setting mode) of the primary transfer unit N1 and the secondary transfer unit N2. ATVC control will be described in detail later. The control unit 30 (more specifically the adjustment process unit 31d) can be controlled to execute an adjustment mode to adjust the setting voltage of the secondary transfer voltage. The adjustment mode will be described in detail later. In this embodiment, the control unit 30 (more specifically, the adjustment process unit 31d) has the function of an execution unit that performs the operation (output mode) of outputting a chart in the adjustment mode described later. In addition, in this embodiment, the sensing unit 3 is an acquisition unit that acquires density information regarding the density of the test image on the chart in the adjustment mode described later. (Detection unit) This constitutes the system. In this embodiment, the control unit 30 (more specifically the adjustment process unit 31d and the secondary transfer voltage storage unit / calculation unit 31f) has the function of a setting unit that sets the secondary transfer voltage based on the concentration information acquired by the acquisition unit.

[0036] Here, the image forming apparatus 1 executes a job (image output operation, print job), which is a series of operations that form and output an image on one or more recording materials S, initiated by a single start instruction. A job generally includes an image forming process, a pre-rotation process, a paper-to-paper process when forming an image on multiple recording materials S, and a post-rotation process. The image forming process is the period during which the electrostatic image, toner image, primary transfer, secondary transfer, and fixing of the toner image are performed for the image to be actually formed and output on the recording materials S. The image forming time (image forming period) refers to this period. More specifically, the timing of the image forming time differs depending on the position where each of these processes—electrostatic image formation, toner image formation, primary transfer, secondary transfer, and fixing of the toner image—is performed. The pre-rotation process is the period during which preparatory operations are performed before the image forming process, from when a start instruction is input until the image is actually formed. The paper-to-paper process (image-to-image process) is the period corresponding to the space between recording materials S when image forming is performed continuously on multiple recording materials S (continuous image forming). The post-rotation process is the period during which the image forming process is followed by tidying up (preparation) operations. The non-image forming period is the period other than the image forming process, and includes the pre-rotation process, inter-paper process, post-rotation process, and pre-multi-rotation process, which is the preparation operation when the image forming apparatus 1 is powered on or when it returns from sleep mode.

[0037] 3. Sensing Unit Configuration Next, we will describe the configuration of the sensing unit 3, which has the function of reading the output chart in the adjustment mode for adjusting the setting voltage of the secondary transfer voltage.

[0038] As shown in Figure 1, the sensing unit 3 is provided with a transport path P through which the recording material S passes. A first line sensor 91 and a second line sensor 92 are provided so as to sandwich the transport path P from both sides. The first line sensor 91 is positioned upstream of the second line sensor 92 in the transport direction of the recording material S, and faces the transport path P from below in Figure 1. The second line sensor 92 is positioned downstream of the first line sensor 91 in the transport direction of the recording material S, and faces the transport path P from above in Figure 1. In this embodiment, when adjusting the secondary transfer voltage for both sides of the recording material S in adjustment mode, the recording material S, which has charts formed on both sides, passes through the transport path P inside the sensing unit 3 with the upper side in Figure 1 being the second side and the lower side in Figure 1 being the first side. In other words, the first line sensor 91 faces the first surface of the recording material S, and the second line sensor 92 faces the second surface of the recording material S, so it is possible to read the chart images (patches) formed on both sides of the recording material S in a single pass over the recording material S.

[0039] Furthermore, a first press roller 93 is positioned opposite the first line sensor 91, and a second press roller 94 is positioned opposite the second line sensor 92. When reading the chart, the first and second press rollers 93 and 94 stabilize the posture of the recording material S, thereby stabilizing the reading result. The recording material S that has passed through the sensing unit 3 is discharged to the discharge section 8.

[0040] For the first and second line sensors 91 and 92, for example, contact image sensors (CIS) can be suitably used. In this embodiment, the first and second line sensors 91 and 92 are each capable of reading the chart at a resolution of approximately 300 dpi. In this embodiment, the image data read by the first and second line sensors 91 and 92 are treated in the control unit 30 as luminance values ​​of 0 to 255 for each of the RGB components.

[0041] As shown in Figure 2, the sensing unit 3 is connected to the control unit 30, and can transmit information (concentration information related to concentration) read by the first and second line sensors 91 and 92 to the control unit 30.

[0042] In this embodiment, the chart is read by the sensing unit 3, but the present invention is not limited to this configuration. For example, the image reading unit 80 may be equipped with a function to read the chart. In that case, the operator sets the chart discharged from the image forming apparatus 1 (printer unit 2) into the image reading unit 80. Alternatively, devices corresponding to the first and second line sensors 91 and 92 may be installed on the transport path of the printer unit 2.

[0043] 4. Control of secondary transfer voltage Next, the control of the secondary transfer voltage will be explained. Figure 3 is a flowchart illustrating the general procedure for controlling the secondary transfer voltage in this embodiment. Generally, there are two methods for controlling the secondary transfer voltage: constant voltage control and constant current control. In this embodiment, constant voltage control is used.

[0044] First, the control unit 30 (image formation preparation process unit 31a) acquires job information from the operation unit 70 or external device 200 and starts the job operation (S101). This job information includes image information specified by the operator and information about the recording material S. This information about the recording material S includes information about the size of the recording material S and information about the type of recording material S (so-called "paper type category") such as "thin paper, plain paper, thick paper, etc.". The type of recording material S includes any information that can distinguish the recording material S, such as attributes based on general characteristics of plain paper, thick paper, thin paper, glossy paper, coated paper, etc., brand name, product number, basis weight, thickness, etc. The control unit 30 (image formation preparation process unit 31a) writes this job information to the RAM 33 (S102).

[0045] Next, the control unit 30 (image formation preparation process unit 31a) acquires environmental information detected by the temperature sensor 71 and the humidity sensor 72 (S103). The ROM 32 also stores information showing the correlation between the environmental information and the target current Itarget for transferring the toner image on the intermediate transfer belt 44b onto the recording material S. Based on the environmental information read in S103, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) determines the target current Itarget corresponding to the environment from the information showing the relationship between the environmental information and the target current Itarget. Then, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) writes this target current Itarget to the RAM 33 (or secondary transfer voltage storage unit / calculation unit 31f) (S104). The reason for changing the target current Itarget according to the environmental information is that the amount of charge of the toner changes depending on the environment. In this embodiment, the target current Itarget is determined in advance using the image forming apparatus 1 to find the secondary transfer current value that allows for the transfer of an image with the maximum toner amount (in this embodiment, a solid secondary color covering the entire surface) for each environment.

[0046] Next, the control unit 30 (ATVC control process unit 31b) acquires information regarding the electrical resistance of the secondary transfer unit N2 by ATVC control (Active Transfer Voltage Control) before the toner image on the intermediate transfer belt 44b and the recording material S to which the toner image is transferred reach the secondary transfer unit N2 (S105). That is, with the secondary transfer outer roller 45b and the intermediate transfer belt 44b in contact, the secondary transfer power supply 76 supplies multiple predetermined voltage levels to the secondary transfer outer roller 45b. The current value while the predetermined voltage is supplied is detected by the current detection sensor 76b, and the relationship between voltage and current (voltage-current characteristics) as shown in Figure 4 is acquired. The control unit 30 (ATVC control process unit 31b) writes this information on the relationship between voltage and current to the RAM 33 (or secondary transfer voltage storage unit / calculation unit 31f). This relationship between voltage and current changes according to the electrical resistance of the secondary transfer unit N2. Alternatively, a predetermined current at multiple levels may be supplied from the secondary transfer power supply 76 to the secondary transfer outer roller 45b, and the voltage value generated at that time may be detected by the voltage detection sensor 76a. In the configuration of this embodiment, the relationship between voltage and current is not such that the current changes linearly (proportionally) with respect to voltage, but rather the current changes in such a way that it can be expressed as a polynomial of order two or higher of the voltage. Therefore, in this embodiment, in order to express the relationship between voltage and current as a polynomial, the predetermined voltage or current supplied when acquiring information on the electrical resistance of the secondary transfer unit N2 is set to three or more multi-stage values.

[0047] Next, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) determines the voltage value to be applied from the secondary transfer power supply 76 to the secondary transfer outer roller 45b (S106). In other words, the control unit 30 determines the voltage value Vb required to flow the target current Itarget in the secondary transfer unit N2 when there is no recording material S, based on the target current Itarget written to the RAM 33 in S104 and the relationship between voltage and current determined in S105. This voltage value Vb corresponds to the secondary transfer partial voltage (transfer voltage due to the electrical resistance of the secondary transfer unit N2). In addition, the ROM 32 stores information for determining the recording material partial voltage (transfer voltage due to the electrical resistance of the recording material S) Vp, as shown in Figure 5. This information is set as table data showing the relationship between the environmental moisture content (absolute moisture content) and the recording material partial voltage Vp for each basis weight category (corresponding to paper type category) of the recording material S. Furthermore, since the electrical resistance of the recording material S increases due to a decrease in moisture content after passing through the fixing device 46, separate tables are prepared for the first and second sides. The control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) calculates the recording material distribution voltage Vp from the table data based on the job information acquired in S101 and the environmental information acquired in S103. The table data for calculating the recording material distribution voltage Vp, as shown in Figure 5, has been determined in advance through experiments, etc. The control unit 30 can also determine the environmental moisture content based on the temperature information acquired by the temperature sensor 71 and the humidity information acquired by the humidity sensor 72. In addition, if an adjustment value has been set by the adjustment mode for adjusting the secondary transfer voltage setting value, which will be described later, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) calculates the adjustment amount ΔV corresponding to that adjustment value. As will be described later, this adjustment value is stored in the RAM 33 (or secondary transfer voltage storage unit / calculation unit 31f) when it has been set by the adjustment mode. The control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) calculates Vb+V+ΔV, which is the sum of Vb, Vp, and ΔV, as the secondary transfer voltage Vtr to be applied from the secondary transfer power supply 76 to the secondary transfer outer roller 45b when the recording material S passes through the secondary transfer unit N2.Then, the control unit 30 (secondary transfer voltage storage unit / calculation unit 31f) writes this Vtr (=Vb+Vp+ΔV) to the RAM 33 (or secondary transfer voltage storage unit / calculation unit 31f).

[0048] Here, the recording material voltage Vp can change not only due to information related to the electrical resistance of the recording material S (such as basis weight), but also due to the surface properties of the recording material S. Therefore, the table data above may be set so that the recording material voltage Vp changes depending on information related to the surface properties of the recording material S. In this embodiment, information related to the electrical resistance of the recording material S (and further information related to the surface properties of the recording material S) is included in the job information acquired in S101. However, the image forming apparatus 1 may be provided with measuring means for detecting the thickness of the recording material S and the surface properties of the recording material S, and the recording material voltage Vp may be determined based on the information obtained by this measuring means.

[0049] Next, the control unit 30 (image forming process unit 31c) performs image formation, sends the recording material S to the secondary transfer unit N2, and controls the system to perform secondary transfer by applying the secondary transfer voltage Vtr determined as described above (S107). After that, the control unit 30 (image forming process unit 31c) repeats S107 until all images of the job have been transferred to the recording material S and output (S108).

[0050] Regarding the primary transfer unit N1, the same ATVC control as described above is performed from the start of the job until the toner image is transported to the primary transfer unit N1, but a detailed explanation is omitted here.

[0051] 5. Overview of Adjustment Modes Next, we will explain the adjustment mode for adjusting the secondary transfer voltage setting voltage. Depending on the type and condition of the recording material S used for image formation, the moisture content and electrical resistance of the recording material S may differ significantly from those of a standard recording material S. In this case, as described above, setting the secondary transfer voltage using the default recording material distribution voltage Vp may not allow for proper transfer.

[0052] First, if the secondary transfer voltage is insufficient, the toner on the intermediate transfer belt 44b cannot be sufficiently transferred to the recording material S, resulting in a decrease in image density. For example, this may occur if the electrical resistance of the recording material S is higher than the value assumed for each paper type category (corresponding to the recording material distribution voltage Vp), or if the moisture content of the recording material S has decreased (dried out) due to storage conditions, causing an increase in electrical resistance. In such cases, it is desirable to increase the setting voltage of the secondary transfer voltage (increase the absolute value) by increasing the recording material distribution voltage Vp.

[0053] Conversely, if the secondary transfer voltage is excessively high, abnormal discharge may occur, resulting in image defects, or the charge of the toner may reverse due to discharge in the secondary transfer section N2, leading to a decrease in transferability. For example, this could occur if the electrical resistance of the recording material S is lower than the value assumed for each paper type category (corresponding to the recording material distribution voltage Vp), or if the moisture content of the recording material S increases (hygroscopic) due to storage conditions, causing a decrease in electrical resistance. In such cases, it is desirable to lower the setting voltage of the secondary transfer voltage (reduce its absolute value) by lowering the recording material distribution voltage Vp.

[0054] Therefore, it is desirable for operators, such as users or service personnel, to adjust (change) the recording material distribution voltage Vp according to the recording material S actually used for image formation, thereby adjusting (changing) the secondary transfer voltage setting voltage during job execution to an optimal value. In other words, it is sufficient to select the optimal recording material distribution voltage Vp + ΔV (adjustment amount) according to the recording material S actually used for image formation. This adjustment can be performed by the following method. For example, the operator can output the image to be output, switching the secondary transfer voltage for each recording material S, and check for any image defects in the output image to determine the optimal secondary transfer voltage setting voltage (more specifically, the recording material distribution voltage Vp + ΔV). However, with this method, the amount of wasted recording material S increases, and it may take a long time, as it involves repeatedly outputting images and adjusting the secondary transfer voltage setting voltage.

[0055] Therefore, in this embodiment, the image forming apparatus 1 is capable of executing an adjustment mode for adjusting the setting voltage of the secondary transfer voltage. In this adjustment mode, a chart is output in which multiple patches of representative colors (test image, test pattern, test toner image) are transferred to the recording material S actually used for image formation, with the setting voltage of the secondary transfer voltage being switched for each patch. Based on the results of reading the output chart by the sensing unit 3, the optimal setting voltage of the secondary transfer voltage (more specifically, the recording material distribution voltage Vp + ΔV) is determined. In particular, in this embodiment, a recommended adjustment amount ΔV (more specifically, the corresponding adjustment value N) for optimizing the image density is presented based on the brightness information (density information) of the patches on the chart. This reduces the need for the operator to visually check for image defects, thereby reducing the operator's workload and enabling more appropriate adjustment of the secondary transfer voltage setting.

[0056] 6. Chart Next, the chart 100 output in the adjustment mode in this embodiment will be described. In this embodiment, different charts 100 are output depending on the size of the recording material S used to output the chart 100. The length of the recording material S in the transport direction is also simply called the "transport direction length," and the length of the recording material S in a direction approximately perpendicular to the transport direction is also simply called the "width." The transport direction of the recording material S is approximately parallel to the sub-scanning direction (the direction of movement of the surface of the photosensitive drum 51 and the intermediate transfer belt 44b), and the direction approximately perpendicular to the transport direction of the recording material S (also called the "width direction" here) is approximately parallel to the main scanning direction (the direction approximately perpendicular to the direction of movement of the surface of the photosensitive drum 51 and the intermediate transfer belt 44b). The lengths in the directions corresponding to the "transport direction length" and "width" of the recording material S are also simply called the "transport direction length" and "width," respectively, for the chart, the image data defining the chart, or the patches formed on the chart.

[0057] Figure 6 is a schematic diagram of a large chart (also called an "L chart") 100L, which is a chart for cases where the transport length of the recording material S is 420 mm (the long side of A3 size) or more, and the width of the recording material S is 279.4 mm (the long side of LTR size) or more.

[0058] The large chart data (also called "L chart data"), which is the image data that defines the L chart 100L, corresponds to the maximum paper size. The image size of the L chart data is approximately 13 inches (≒330 mm) in width and 19.2 inches (≒487 mm) in length in the transport direction. Depending on the size of the recording material S, the L chart 100L corresponding to the image data cut from this L chart data is output. At this time, the image data is cut from the L chart data to match the size of the recording material S, with the leading edge in the reading direction and the center in the width direction as the reference point. Figure 6 shows the case where the size of the recording material S is A3 size (portrait feed). For example, if the recording material S used to output the L chart 100L is A3 size (portrait feed) (width 297 mm × transport direction length 420 mm), then image data with a size of 292 mm in width and transport direction length 415 mm is cut from the L chart data. Then, an image corresponding to this cropped image data is formed on an A3-sized (portrait orientation) recording material S, with a margin of 2.5 mm at each end, based on the leading edge in the reading direction and the center in the width direction. This margin is typically around 2 to 10 mm.

[0059] In the L-chart 100L, a total of 11 sets of blue (B) solid patches 101, black (Bk) solid patches 102, and black halftone (BkHT) patches 103 are arranged in a line in the width direction, along the transport direction of the recording material S. In this embodiment, when the output of the exposure device 42 is 0 when no image is formed, and the output of the exposure device 42 is 255 when an image of the Bk solid patch 102 is formed, the output of the exposure device 42 is 128 when an image of the BkHT patch 103 is formed. A solid patch (solid image) is an image with the maximum amount of toner applied. A halftone patch (halftone image) can be formed with a toner application amount of about 10-80% when the toner application amount of a solid image is set to 100%, and is typically formed with a toner application amount of about 40-60%. In the L-chart 100L in Figure 6, 100L(1) shows the first side, and 100L(2) shows the second side. The second face passes through the secondary transfer section N2 and then through the inside of the sensing unit 3 without changing orientation, but the first face passes through the reversal transport path 7 once. Therefore, the orientation of the first face is different when passing through the secondary transfer section N2 and when passing through the inside of the sensing unit 3. In Figure 6, the transport direction of the chart when passing through the secondary transfer section N2 is shown by a thin arrow, and the transport direction of the chart when passing through the inside of the sensing unit 3 is shown by a thick arrow. In this embodiment, the leading patches of the B solid patch 101, Bk solid patch 102, and BkHT patch 103 when passing through the inside of the sensing unit 3 are position information acquisition patches (also called "trigger patches" here) 101T, 102T, and 103T, respectively. These trigger patches 101T, 102T, and 103T are used to accurately detect the position of the patch row when read by the first and second line sensors 91 and 92. Of the B solid patch 101, Bk solid patch 102, and BkHT patch 103, the remaining 10 patches each, excluding the trigger patches 101T, 102T, and 103T, are the patches 101A, 102A, and 103A used for acquiring brightness information (density information) (also referred to here as "adjustment patches"). Each of the adjustment patches 101A, 102A, and 103A is applied to the recording material S with a different secondary transfer voltage Vtr.

[0060] In this embodiment, the size of each patch (adjustment patch, trigger patch) is approximately 15 mm in length and 15 mm in width in the transport direction, and there is a 15 mm gap between the patches in the transport direction of the recording material S. Furthermore, in the first side 100L(1) and the second side 100L(2) of the L chart 100L, patches 101 to 103 are arranged so that they do not overlap on the front and back sides of the recording material S. This is to avoid the effect of back-image bleed-through on the detection brightness when read by the first and second line sensors 91 and 92. This effect of back-image bleed-through on the detection brightness is a concern, especially when the recording material S is thin paper with a low basis weight.

[0061] Figure 7 is a schematic diagram showing a small chart (also called an "S chart") 100S, which is a chart for cases where the transport length of the recording material S is 210 mm (short side of A4 size) or more and less than 420 mm (long side of A3 size), and the width of the recording material S is 279.4 mm (long side of LTR size) or more.

[0062] The small chart data (also called "S chart data"), which is the image data that defines the S chart 100S, corresponds to half the size of the maximum paper size. The image size of the S chart data is approximately 13 inches (≒330 mm) in width and 9.6 inches (≒243 mm) in length in the transport direction. When the size of the recording material S is A4 (landscape feed) or LTR (landscape feed), the S chart 100S corresponding to the image data cut from this S chart data is output according to the size of the recording material S. At this time, the image data is cut from the S chart data to match the size of the recording material S, with the leading edge in the reading direction and the center in the width direction as the reference point. Figure 7 shows the case when the size of the recording material S is A4 size (landscape feed). For example, when the recording material S used to output the S chart 100S is A4 size (landscape feed) (length in transport direction 210 mm × width 297 mm), image data with a size of 205 mm in length in the transport direction × width 292 mm is cut from the S chart data. Then, an image corresponding to this cropped image data is formed on an A4-sized (landscape orientation) recording material S, with a margin of 2.5 mm at each end, based on the leading edge in the reading direction and the center in the width direction. This margin is typically around 2 to 10 mm.

[0063] In the S chart 100S, a total of 12 sets of blue (B) solid patches 101, black (Bk) solid patches 102, and black halftone (BkHT) patches 103 are arranged side by side in the width direction, spanning two recording materials S and in the direction of transport of the recording materials S. In the S chart 100S, by using two recording materials S to form the chart, the same number of patches as the L chart 100L is secured, and equivalent adjustments can be made. In the S chart 100S in Figure 7, 100S(1-1) shows the first sheet of the first side, 100S(1-2) shows the second sheet of the first side, 100S(2-1) shows the first sheet of the second side, and 100S(2-2) shows the second sheet of the second side. After the second side passes through the secondary transfer section N2, it passes through the inside of the sensing unit 3 without changing orientation, but the first side passes through the reversal transport path 7 once. Therefore, the orientation of the first surface differs when passing through the secondary transfer section N2 and when passing through the inside of the sensing unit 3. In Figure 7, the transport direction of the chart when passing through the secondary transfer section N2 is indicated by a thin arrow, and the transport direction of the chart when passing through the inside of the sensing unit 3 is indicated by a thick arrow. In this embodiment, with respect to the patches formed on one surface of the recording material S, the leading patches of the B solid patch 101, Bk solid patch 102, and BkHT patch 103 when passing through the inside of the sensing unit 3 are trigger patches 101T, 102T, and 103T for acquiring position information, respectively. These trigger patches 101T, 102T, and 103T are used to accurately detect the position of the patch row when read by the first and second line sensors 91 and 92. Of the B solid patch 101, Bk solid patch 102, and BkHT patch 103, the remaining 10 patches each, excluding the trigger patches 101T, 102T, and 103T, are adjustment patches 101A, 102A, and 103A for acquiring brightness information (density information). Each of the adjustment patches 101A, 102A, and 103A is applied to the recording material S with a different secondary transfer voltage Vtr.

[0064] As described above, in this embodiment, the size of each patch (adjustment patch, trigger patch) is approximately 15 mm in length and 15 mm in width in the transport direction, and the patches are spaced 15 mm apart in the transport direction of the recording material S. Furthermore, in the first side 100S(1-1), 100S(1-2) and the second side 100S(2-1), 100S(2-2) of the S chart 100S, patches 101 to 103 are arranged so that they do not overlap on the front and back sides of the recording material S. This is to avoid the effect of back-printing on the detection brightness when read by the first and second line sensors 91 and 92. This effect of back-printing on the detection brightness is a concern, especially when the recording material S is thin paper with a low basis weight.

[0065] The size of each patch (especially the adjustment patch) should be somewhat large in area, taking into account the readings from the first and second line sensors 91 and 92. However, if the size of each patch (especially the adjustment patch) is made too large, the number of secondary transfer voltages Vtr that can fluctuate within the chart will decrease. In this embodiment, the patch size is set so that the secondary transfer voltage Vtr can fluctuate in 10 steps in the L chart 100L. Furthermore, the patch spacing in the transport direction of the recording material S should be set so that the secondary transfer voltage can be switched.

[0066] Furthermore, it is preferable to prevent the formation of patches near the leading and trailing ends of the recording material S in the transport direction (for example, within a range of about 10 mm inward from the edge). This is because image defects may occur only at the leading or trailing end of the recording material S, making it difficult to determine whether or not they are caused by the secondary transfer voltage.

[0067] Furthermore, in this embodiment, the size of the recording material S that can be used for chart output is set to a length of 210 mm (short side of A4 size) or more in the transport direction and a width of 279.4 mm (long side of LTR size) or more. In this embodiment, as long as it is larger than this size, recording material S of any size can be used, not only in standard sizes, but also by the operator specifying it by inputting it from the control unit 70 or external device 200. Note that the size of the recording material S that can be used for chart output is not limited to that of this embodiment and can be set as appropriate according to the maximum paper feed size of the image forming apparatus 1, etc.

[0068] Furthermore, in this embodiment, when adjusting the secondary transfer voltage (only the secondary transfer voltage during single-sided printing) for only one side of the recording material S (also referred to here as "single-sided adjustment"), the following procedure is followed. When outputting the L chart 100L, the chart 100L(2) in Figure 6 is formed on the first side of one recording material S using a single-sided printing image forming operation and output. When outputting the S chart 100S, the chart 100S(2-1) and the chart 100S(2-2) in Figure 7 are formed on the first side of the first recording material S and the first side of the second recording material S, respectively, using a single-sided printing image forming operation and output. In other words, when adjusting the secondary transfer voltage (secondary transfer voltage for the first and second sides during double-sided printing) for both sides of the recording material S (also referred to here as "double-sided adjustment"), the chart for the second side is output using a single-sided printing image forming operation without passing through the inverted transport path 7. Furthermore, the chart is read using the second line sensor 92 of the sensing unit 3. This allows single-sided adjustment to be performed with minimal downtime (time when the image cannot be output for adjustment, etc.) because the orientation of the read image does not change from that during double-sided adjustment, and the recording material S does not pass through the inversion transport path 7. In addition, the adjustment result of the first side during double-sided adjustment can also be used to set the secondary transfer voltage during single-sided printing.

[0069] Furthermore, the chart design is not limited to that of this embodiment. For example, the adjustment patch is not limited to using a solid B image, a solid Bk image, and a solid BkHT image. For example, the solid patch may be either a solid B image or a solid Bk image, or it may be any other solid color image, a solid image of another secondary color, or a solid image of a multi-order color, either alone or in combination. Also, the halftone patch is not limited to black, but may be a solid color halftone image of another secondary color, or a solid image of a multi-order color. Furthermore, the density of the halftone patch is not limited to that of this embodiment. In addition, the color and density of the patch may be changed, for example, according to the image actually output by the user. Such changes can be made, for example, from the operation unit 70 or an external device 200. Furthermore, the shape and number of adjustment patches may also be changed according to the configuration of the image forming apparatus 1, the size of the recording material S corresponding to the chart output, the reading method, etc. Furthermore, the shape of the trigger patch, etc., is not limited to that of this embodiment. Furthermore, depending on the chart reading method, trigger patches may not always be necessary.

[0070] Furthermore, assuming that the operator will visually confirm the settings, information such as the patch number described later may be printed on each set of patches in relation to the transport direction of the recording material S, as identification information indicating the setting of the secondary transfer voltage when transferring each patch to the recording material S. Also, assuming that the operator will visually confirm the settings, information such as the front side (first side) and the back side (second side) may be printed on the corresponding side as identification information indicating whether it is the adjustment chart for the first side or the adjustment chart for the second side.

[0071] 7. Operation of adjustment mode Next, the operation of the adjustment mode in this embodiment will be described. FIG. 8 is a flowchart showing an outline of the procedure of the adjustment mode in this embodiment. Here, a case where an operator causes the image forming apparatus 1 to execute the adjustment mode via the operation unit 70 of the image forming apparatus 1 will be described as an example. The role of the operation unit 70 for causing the image forming apparatus 1 to execute the adjustment mode may be performed by an external device 200 such as a personal computer. Also, the following symbols will be used in the following description.

[0072] N: Adjustment value (=-20 to +20) N0: Current (before execution of adjustment mode) adjustment value N A : Selected adjustment value n: Patch number of adjustment patch (n = 1 to 10 in ascending order of adjustment value) n0: Patch number corresponding to the current adjustment value (corresponding to the adjustment value N0) n A : Selected patch number (corresponding to the adjustment value N A corresponding to) T: Symbol indicating a trigger patch

[0073] First, the control unit 30 (adjustment process unit 31d) acquires information on the recording material S that the operator wants to adjust (size of recording material S, paper type category) and information on adjustment conditions, which are input by the operator (S1). Figure 9 is a schematic diagram of the paper type category selection screen 700 displayed on the display unit 70a of the operation unit 70 under the control of the control unit 30 (adjustment process unit 31d) in S1. The paper type category selection screen 700 displays the paper type categories of the recording material S that can be set in the image forming apparatus 1. By pressing (operating) the adjustment button 701, the operator can proceed to the adjustment mode to adjust the setting voltage of the secondary transfer voltage. Note that the paper type category selection screen 700 may also provide access to screens for changing other image forming conditions, such as fixing conditions, in addition to adjusting the secondary transfer voltage. Furthermore, in order to retain the default settings for each paper type category, the paper type categories may be duplicated to RAM 33 or ROM 32 using the duplicate button 702 before the adjustment mode can be executed. The duplicated paper type category 703 is saved under a different name in RAM33 or ROM32, and for that paper type category 703, image formation will be performed using the default settings, except for conditions where the settings have been changed.

[0074] Figure 10 is a schematic diagram of the paper feed unit selection screen 704 displayed on the display unit 70a of the operation unit 70 under the control of the control unit 30 (adjustment process unit 31d) in S1. When the paper type category of the recording material S for which the adjustment mode is executed is selected, the paper feed unit selection screen 704 shown in Figure 10 is displayed. The paper feed unit selection screen 704 displays the paper type category of the recording material S stored in the paper feed unit 4, which has been set in advance by the operator from the operation unit 70 or the like, and the size detected by the recording material size detection sensor (not shown) provided in each paper feed unit 4. For example, "Plain paper 1_copy (64~75g / m²)" 2 This section describes the case where ")" is selected and the adjustment mode is executed. In the example in Figure 10, multiple paper feeders (paper feeder [1], paper feeder [2], paper feeder [3] in Figure 10) are set to "Plain paper 1_copy (64~75g / m²)". 2) is stored therein. Also, when the size of the recording material S is compatible with the adjustment mode (paper feed unit [1], paper feed unit [2] in Figure 10), the operator can press (operate) the selection button 705. If the paper type category or the size of the recording material S is not compatible with the adjustment mode, the selection button 705 may be grayed out so that the operator cannot press (operate) it. Also, if the recording material S required to execute the adjustment mode is not already stored in any of the paper feed units 4, the operator may be able to exit the paper feed unit selection screen 704 by pressing a back button (not shown) or the like.

[0075] Figure 11 is a schematic diagram of the secondary transfer voltage adjustment screen 706 displayed on the display unit 70a of the operation unit 70 under the control of the control unit 30 (adjustment process unit 31d) in S1. When the paper type category of the recording material S on which the adjustment mode is to be executed is selected, and the paper feed unit 4 on which the recording material S is stored is selected, the secondary transfer voltage adjustment screen 706 shown in Figure 11 is displayed. The secondary transfer voltage adjustment screen 706 includes an adjustment value display unit 707 that displays the current adjustment value, a single-sided / double-sided selection unit 708a that selects whether the target of the adjustment mode is single-sided or double-sided, and so on. The secondary transfer voltage adjustment screen 706 also includes a priority image selection unit 708b that selects the density of the image to be optimized in the adjustment mode, and an adjustment execution button 709 that starts the formation of a chart. As will be described in detail later, in this embodiment, the priority image selection unit 708b can select the priority image from two options: "midtones" and "solid images". By inputting a value into the adjustment value display unit 707, secondary transfer becomes possible with the recording material distribution voltage offset from the default recording material distribution voltage Vp stored in the ROM 32 for the corresponding paper type category. In this embodiment, the adjustment value display unit 707 can accept integer values ​​from -20 to +20 as the adjustment value N, and the default value is 0. If the adjustment value N is 0, the default recording material distribution voltage Vp corresponding to the paper type category stored in the ROM 32 is used as is. The value of the adjustment value display unit 707 (adjustment value N) corresponds to ΔN=1 = ΔV=150V (that is, changing the adjustment value N by 1 changes the adjustment amount ΔV by 150V). For example, if N=-5 is input to the adjustment value display unit 707, the recording material distribution voltage used will be the default recording material distribution voltage Vp offset by -750V (=-5 × 150). When the operator performs the adjustment mode, they select whether to perform a double-sided or single-sided adjustment using the single-sided / double-sided selection unit 708a, select the preferred image using the priority image selection unit 708b, and then press the adjustment execution button 709 (perform the operation). The inputs from the single-sided / double-sided selection unit 708a and the priority image selection unit 708b are stored in the RAM 33. In this way, the inputs made during the determination of the adjustment conditions (S1) are stored in the RAM 33 and reflected in subsequent processing.

[0076] The control unit 30 (adjustment process unit 31d) executes density correction control (S2) when the adjustment execution button 709 is pressed (operated). Density correction control is performed to ensure that an appropriate amount of toner is placed on the intermediate transfer belt 44b before adjusting the secondary transfer voltage. The control unit 30 (adjustment process unit 31d) forms toner patches for density correction control by changing the output of the charging power supply 73, developing power supply 74, exposure device 42, etc., and controls them to be primary transferred onto the intermediate transfer belt 44b. The control unit 30 (adjustment process unit 31d) then determines the image formation conditions for chart output by measuring the amount of toner on the toner patches on the intermediate transfer belt 44b using a patch detection sensor (not shown). Note that density correction control does not necessarily need to be performed every time the adjustment mode is executed. The control unit 30 (adjustment process unit 31d) may decide whether or not to perform density correction control based on, for example, the number of images formed, environmental changes, elapsed time, etc., since the last time density correction control was performed.

[0077] Subsequently, the control unit 30 (adjustment process unit 31d, ATVC control process unit 31b) executes ATVC control (S3). Details of the ATVC control are as described above.

[0078] Subsequently, the control unit 30 (adjustment process unit 31d) executes the output of a chart (S4). At this time, the control unit 30 (adjustment process unit 31d) selects a chart according to the size of the recording material S and outputs the selected chart.

[0079] Figure 12 is a graph showing the output of the secondary transfer power supply 76 when forming the L chart 100L. Figure 12(a) shows the first side during double-sided adjustment, and Figure 12(b) shows the second side during double-sided adjustment. In the case of the first side, adjustment patches 101A to 103A are each secondarily transferred to the recording material S in a sequence of 10, after which trigger patches 101T to 103T are each secondarily transferred to the recording material S. The adjustment patches 101A to 103A are arranged so that the adjustment value N increases sequentially from the smallest adjustment value N. The patch numbers of adjustment patches 101A to 103A are set so that the patch number corresponding to the smallest adjustment value N is n=1, the patch number corresponding to the largest adjustment value N is n=10, and so on, increasing sequentially in accordance with the increase in adjustment value N. Also, in the case of the first side, the recording material distribution voltage Vp for setting the secondary transfer voltage Vtr is the value of the table stored in ROM 32 for the first side. When the chart is transferred to the recording material S, the timing of the secondary transfer voltage switching occurs after each patch 101-103 has passed through the secondary transfer. There is a slight time lag before the output of the secondary transfer power supply 76 switches, but by switching at the above timing, the output of the secondary transfer power supply 76 switches in the gaps between each patch. In the case of the second side, the arrangement of the adjustment patches 101A-103A and the trigger patches 101T-103T is reversed compared to the first side, and the value of the recording material distribution voltage Vp used is the value of the table stored in ROM 32 for the second side. However, the switching of the secondary transfer voltage and other operations are performed in the same way as the first side.

[0080] In this embodiment, the amplitude (change in one step) ΔV (indicated by 801 in Figure 12) of the secondary transfer voltage when the chart is transferred to the recording material S is switched by the secondary transfer partial voltage Vb. In this embodiment, when the secondary transfer partial voltage Vb is 2000V or higher, the amplitude ΔV of the secondary transfer voltage is set to 450V, which corresponds to the adjustment value amplitude ΔN=3 (three steps of the adjustment value N). When the secondary transfer partial voltage Vb is 1500V or higher and less than 2000V, the amplitude ΔV of the secondary transfer voltage is set to 300V, which corresponds to the adjustment value amplitude ΔN=2 (two steps of the adjustment value N). When the secondary transfer partial voltage Vb is less than 1500V, the amplitude ΔV of the secondary transfer voltage is set to 150V, which corresponds to the adjustment value amplitude ΔN=1 (one step of the adjustment value N). This is because, in order to confirm the current sensitivity of the secondary transfer, it is considered more efficient to increase the range of change in the secondary transfer voltage in one step as the secondary transfer partial voltage Vb increases, thereby widening the range of change in the secondary transfer current across the entire chart. In this embodiment, the amplitude ΔV (swing amplitude ΔN of the adjustment value) of the secondary transfer voltage when the chart is transferred to the recording material S is automatically selected according to the result of ATVC control, but it may also be possible to allow the operator to directly select it on the secondary transfer voltage adjustment screen 706 or the like. Furthermore, it may also be possible to allow the operator to choose whether to "automatically select" or "directly specify" the amplitude ΔV (swing amplitude ΔN of the adjustment value) of the secondary transfer voltage when the chart is transferred to the recording material S.

[0081] Figures 13(a) to 13(c) show a list of the current adjustment value N0 and the adjustment value N of the secondary transfer voltage applied to each patch number n, for each adjustment value amplitude ΔN (secondary transfer voltage amplitude ΔV) and for each of the first and second faces in this embodiment. Figure 13(a) shows the case when the adjustment value amplitude ΔN=1, Figure 13(b) shows the case when the adjustment value amplitude ΔN=2, and Figure 13(c) shows the case when the adjustment value amplitude ΔN=3. When the current adjustment value N0 is 0, patch number n=5 corresponds to the current adjustment value N0=0, n=1 to 4 correspond to the smaller adjustment value side at ΔN intervals, and n=6 to 10 correspond to the larger adjustment value side at ΔN intervals. When the current adjustment value N0 is not 0, the adjustment values ​​corresponding to each adjustment patch 101A to 103A are uniformly offset. Furthermore, if the current adjustment value N0 is fixed at n=5, there will be cases where all adjustment patches 101A~103A for n=1~10 do not fall within the ±20 adjustment range if the current adjustment value N0 is large on the positive or negative side. In such cases, the patch corresponding to the current adjustment value N0 is shifted from n=5 to ensure that all adjustment patches 101A~103A for n=1~10 fall within the ±20 adjustment range. This ensures that all adjustment patches 101A~103A can be effectively utilized.

[0082] In the case of L Chart 100L, when the chart is secondarily transferred to the recording material S, trigger patches 101T to 103T are located on the trailing edge of the first sheet and the leading edge of the second sheet. Trigger patches 101T to 103T are used for detecting the position of the patches when the sensing unit 3 reads the chart. Therefore, trigger patches 101T to 103T need to be transferred with the minimum density required for this purpose. Extremely high or extremely low secondary transfer voltages pose a risk of preventing the reading of trigger patches 101T to 103T. For this reason, in this embodiment, when secondarily transferring trigger patches 101T to 103T to the recording material S, a voltage corresponding to patch number n=5 (the voltage indicated by the dotted line of reference numeral 800 in Figure 12) is applied. Note that the method for setting the secondary transfer voltage applied when secondarily transferring trigger patches 101T to 103T to the recording material S is not limited to the method of this embodiment described above. For example, one could set the secondary transfer voltage higher (to a larger absolute value) to minimize weak transfer (transfer failure due to a weak transfer voltage), or control the secondary transfer voltage with a constant current to transfer at the minimum required concentration.

[0083] Figure 14 is a graph showing the output changes of the secondary transfer power supply 76 when forming the S chart 100S. Figure 14(a) shows the first side when both sides are adjusted, and Figure 14(b) shows the second side when both sides are adjusted. In the case of the S chart 100S, it is divided into the first sheet 100S (1-1) of the first side, the second sheet 100S (1-2) of the first side, the first sheet 100S (2-1) of the second side, and the second sheet 100S (2-2) of the second side, with trigger patches 101T to 103T placed on each. However, even in the case of the S chart 100S, the magnitude and timing of the output of the secondary transfer power supply 76 basically operate in the same way as in the case of the L chart 100L.

[0084] As mentioned above, if the operator selects single-sided adjustment in the single-sided / double-sided selection section 708a of the secondary transfer voltage adjustment screen 706, the following procedure is followed: When outputting the L chart 100L, the chart 100L(2) in Figure 6 is output. When outputting the S chart 100S, the charts 100S(2-1) and 100S(2-2) in Figure 7 are output. In other words, the chart for the second side when performing double-sided adjustment is output without passing through the inversion transport path 7 during the single-sided print image formation operation. The chart is read using the second line sensor 92 of the sensing unit 3. This allows single-sided adjustment to be performed with minimal downtime, as the orientation of the read image does not change from that during double-sided adjustment, and the recording material S does not pass through the inversion transport path 7.

[0085] When the control unit 30 (adjustment process unit 31d) outputs a chart, it first determines whether or not the high voltage (secondary transfer voltage) is saturated (S5). "High voltage saturation" refers to a state in which the secondary transfer voltage Vtr has reached (is stuck to) the upper or lower limit of the output voltage of the secondary transfer power supply 76. The secondary transfer power supply 76 has an upper limit of output voltage, and although it depends on the specifications of the high-voltage power supply, in this embodiment the upper limit of the output voltage (absolute value) of the secondary transfer voltage 76 is 6.5kV.

[0086] For example, if the secondary transfer outer roller 45b is used for a long period of time, or if the operating environment of the image forming apparatus 1 is a low-temperature, low-humidity environment, the electrical resistance of the secondary transfer section N2 increases, and the secondary transfer partial voltage Vb increases (its absolute value becomes large). Another example is if the current adjustment value N0 is extremely large, such as +20. In this case, the adjustment is performed around the current adjustment value N0 = +20, which inevitably increases the secondary transfer voltage Vtr (its absolute value becomes large). In such cases, the secondary transfer voltage Vtr reaches the output limit of the secondary transfer power supply 76, and the secondary transfer voltage cannot be adjusted when outputting the chart. The control unit 30 (adjustment process section 31d) determines that if the secondary transfer voltage Vtr for all adjustment patches 101A to 103A (patch number, adjustment value) has reached the output limit of the secondary transfer power supply 76, adjustment itself is impossible, and therefore the smallest adjustment value (N) in the chart is used.A The value is determined to be the smallest N in the chart (S6). The reason for selecting the smallest adjustment value is to increase the possibility of selecting an adjustment value far from the upper limit of the output of the secondary transfer power supply 76 when adjustment is made again. At this time, the control unit 30 (adjustment process unit 31d) may also display a message such as "optimal adjustment could not be performed" or "check the lifespan of the secondary transfer outer roller" on the operation unit 70 or external device 200. In this way, the control unit 30 (adjustment process unit 31d) may control the system to notify that the adjustment of the secondary transfer voltage could not be performed properly.

[0087] Furthermore, if the operating environment of the image forming apparatus 1 is a high-temperature, high-humidity environment, the default recording material distribution voltage Vp is low (small absolute value), and as a result of offsetting the adjustment value to the negative side, the secondary transfer voltage Vtr may become negative. Also, if the current adjustment value N0 is extremely small, such as -20, the adjustment will be performed around the current adjustment value N0 = -20, so the secondary transfer voltage Vtr will inevitably become low (small absolute value). In the configuration of this embodiment, it is theoretically unlikely that a negative secondary transfer voltage Vtr would be optimal, so in this embodiment, Vtr is limited to 0V or higher. The control unit 30 (adjustment process unit 31d) checks if the secondary transfer voltage Vtr for all adjustment patches 101A to 103A (patch number, adjustment value) is 0V, and therefore adjustment itself is impossible, so it checks the largest adjustment value (N) in the chart. AThe value is determined to be the largest N in the chart (S6). The reason for choosing the largest adjustment value is to increase the possibility of selecting an adjustment value that results in a secondary transfer voltage Vtr of 0V or higher when adjustment is made again. At this time, the control unit 30 (adjustment process unit 31d) may also display a message such as "optimal adjustment could not be performed" on the operation unit 70 or external device 200. In this way, the control unit 30 (adjustment process unit 31d) may be controlled to notify that the adjustment of the secondary transfer voltage could not be performed appropriately. In this embodiment, the restriction is made that the secondary transfer voltage Vtr is 0 or higher, but other restrictions may be made. For example, if there is a lower limit value that can be stably applied as the secondary transfer voltage, it may be a value other than 0V. Alternatively, the recording material distribution voltage Vp may be restricted to not being negative, and the lower limit of the secondary transfer voltage Vtr may be set as the secondary transfer unit voltage Vb.

[0088] The control unit 30 (adjustment process unit 31d) proceeds to process S7 if some or all of the adjustment patches 101A to 103A (patch number, adjustment value) are not in a "high-voltage saturation" state. In this embodiment, if some of the adjustment patches 101A to 103A are in a "high-voltage saturation" state, the control unit 30 (adjustment process unit 31d) controls the system so that their adjustment values ​​N are not included as candidates for the recommended secondary transfer voltage adjustment value N in subsequent processing. This is to avoid secondary transfer being performed with a recording material distribution voltage Vp different from the adjustment value N determined in the adjustment mode when the secondary transfer distribution voltage Vb fluctuates. In other words, with an adjustment value N in a "high-voltage saturation" state, it may become impossible to set an appropriate secondary transfer voltage Vtr if the operating environment changes.

[0089] Next, the control unit 30 (adjustment process unit 31d) determines whether the current is fluctuating correctly (S7). In this embodiment, for this determination, the control unit 30 (adjustment process unit 31d) uses the current detection sensor 76b to obtain the current flowing through the secondary transfer unit N2 when each adjustment patch 101A to 103A passes through the secondary transfer unit N2 during chart output, and stores it in the RAM 33. In this embodiment, the method for this determination is as follows.

[0090] I(n): Current of the nth adjustment patch α: coefficient Let n = 1 to 9 I(n+1)≧I(n)×α

[0091] In the above equation, α is a coefficient approximately 1. In other words, the control unit 30 (adjustment process unit 31d) checks whether the secondary transfer current I(n+1) (absolute value) of the (n+1)th adjustment value, which has a larger secondary transfer voltage Vtr than the secondary transfer current I(n) (absolute value) of the nth adjustment value, is α times or more greater. If the above equation does not hold, it is highly likely that the secondary transfer current of each adjustment patch 101A to 103A (patch number, adjustment value) is not fluctuating correctly within the plane of the chart. Possible cases of this include when the electrical resistance within the plane of the recording material S is non-uniform, or when the electrical resistance of the recording material S is extremely low, causing current to flow through the recording material S to components (such as transport rollers and guides) that are in contact with the recording material S near the secondary transfer unit N2. In such cases, the control unit 30 (adjustment process unit 31d) determines that adjustment itself is difficult and terminates the adjustment mode with the current adjustment value (S8). In this embodiment, α is set to 1. However, α does not necessarily have to be 1. For example, by making it greater than 1, adjustment may be performed only when the current is definitely fluctuating. Also, α may be set to different values ​​for the first and second surfaces. In particular, for the first surface, where there may be significant variations in moisture content depending on the storage conditions of the recording material S, α may be less than 1. Furthermore, if the above formula does not hold, the control unit 30 (adjustment process unit 31d) may display a message on the operation unit 70 such as "Optimal adjustment could not be performed" or "There is a possibility that the recording material S cannot be adjusted." In this way, the control unit 30 (adjustment process unit 31d) may control the system to notify that there is a possibility that the adjustment of the secondary transfer voltage could not be performed properly.

[0092] Once the control unit 30 (adjustment process unit 31d) confirms that the current is swinging as intended, it reads the chart using the sensing unit 3 and controls it to calculate the brightness and dispersion of each adjustment patch 101A to 103A as described later (S9).

[0093] The first and second line sensors 91 and 92 of the sensing unit 3 read the first and second charts at a resolution of 300 dpi, respectively. The image information read by the first and second line sensors 91 and 92 of the sensing unit 3 is stored in the RAM 33. The control unit 30 (adjustment process unit 31d) calculates the positions of each adjustment patch 101A to 103A based on the positions of the trigger patches 101T to 103T of the chart as follows. Figure 15 is a schematic diagram illustrating an example of how to identify the positions of trigger patches 101T to 103T from the images 110 read by the first and second line sensors 91 and 92. L chart 100L(2) is used as an example. First, in the transport direction of the recording material S as it passes through the inside of the sensing unit 3, the line 112 located in the margin between the edge 111 of the chart (recording material S) and the trigger patches 101T to 103T is set based on the approximate positional relationship. Then, the average brightness value of line 112 is read from the information read from the chart. At this time, if the average brightness value is smaller than a predetermined threshold (if the density is larger than a predetermined value), it is determined to be an edge of trigger patches 101T to 103T. If it is not determined to be an edge, the process is repeated line by line towards the upstream direction of transport of the recording material S as it passes through the inside of the sensing unit 3 to find the edge line 113. Next, in the width direction, line 114 located in the margin between the edge 111 of the chart (recording material S) and trigger patch 103T is set based on the approximate positional relationship. Then, the average brightness value of line 114 is read from the information read from the chart. At this time, if the average brightness value is smaller than a predetermined threshold (if the density is larger than a predetermined value), it is determined to be an edge of trigger patch 103T. If it is not determined to be an edge, the process is repeated line by line towards the right in the width direction in Figure 15 to find the edge line 115. In Figure 15 above, the right side in the width direction is the right side when the leading edge of the recording material S in the transport direction is facing upwards as it passes through the inside of the sensing unit 3, and the first and second line sensors 91 and 92 sides of the recording material S are viewed. In addition, similar edge detection is performed in the width direction between trigger patches 103T and 102T, and between 102T and 101T.The above edge detection method makes it possible to detect the positions of trigger patches 101T to 103T in image 110. Note that the above edge detection method is just one example, and the edge detection method is not limited to this method. For example, a different method may be used depending on the chart design.

[0094] Once the control unit 30 (adjustment process unit 31d) has identified the location of each adjustment patch 101A to 103A, it calculates the average luminance value and variance value for each adjustment patch 101A to 103A and stores them in the RAM 33. In other words, for the nth adjustment patch, the average luminance value and variance value calculated using the following formula are stored in the RAM 33.

[0095]

number

[0096] In this embodiment, B(m) is detected as a signal value ranging from low brightness 0 to high brightness 255. The average brightness value is a parameter that reflects (i.e., correlates with) density (lower brightness indicates higher density). Furthermore, the inventors' research has shown that the variance value is a parameter that is sensitive to the transferability when the recording material S has irregularities. For both the average brightness value and the variance value, smaller values ​​indicate better transferability. In this embodiment, we will mainly describe a method for determining the recommended adjustment amount ΔV (more specifically, the corresponding adjustment value N) of the secondary transfer voltage setting voltage using the average brightness value, but the variance value may also be used as described later. Note that if only one of the average brightness value or the variance value is used, the calculation of the other value does not need to be performed.

[0097] In this embodiment, the brightness read from the image information read by the sensing unit 3 is B (blue) brightness for the B solid patch 101 and G (green) brightness for the Bk solid patch 102 and BkHT patch 103. The choice of which RGB brightness to use does not have to be as shown, and the average value of the three brightness levels or the grayscale brightness that is not decomposed into RGB may also be used.

[0098] Furthermore, when calculating the variance value, it is necessary to temporarily store the brightness of each read pixel, which may lead to a high load on the control unit 30 and a prolonged adjustment mode. In such cases, the brightness from 0 to 255 may be divided into several categories, the frequency of each pixel may be counted, and the variance value may be calculated from a digital histogram. The number of brightness categories and the spacing between them can be appropriately changed depending on the characteristics of the first and second line sensors 91 and 92 and the processing capacity of the control unit 30. Also, since the brightness histogram differs depending on the paper type category, the number of brightness categories and the spacing between them may be changed according to the paper type category.

[0099] Next, the control unit 30 (adjustment process unit 31d) proceeds to select a patch (patch number, adjustment value) with good transferability using the calculated average brightness value and variance value (in this embodiment, the average brightness value in particular). In this embodiment, at this time, the control unit 30 (adjustment process unit 31d) refers to the input result of the priority image selection unit 708b stored in RAM 33 (S10). Specifically in this embodiment, in S10, it is determined whether or not the midtone priority mode is selected.

[0100] In other words, as mentioned above, generally, the higher the density of the toner image to be transferred, the larger the absolute value of the secondary transfer voltage required. However, when using recording materials S with difficult transfer properties, for example, it may be difficult to transfer images from halftones to solid colors well with a single secondary transfer voltage. An example of recording materials S with difficult transfer properties is embossed paper, which has a more pronounced surface irregularity than plain paper. In the case of embossed paper, a gap is easily created between the intermediate transfer belt 44b and the surface of the paper in the secondary transfer section N2 due to the indentations on the paper surface. When the secondary transfer voltage is high (large absolute value), the image density tends to become lighter due to the discharge effect in this gap. This effect can be particularly noticeable in halftone images, where the amount of toner applied is less than in solid colors. Therefore, for example, when outputting halftone images using such recording materials S, adjusting the secondary transfer voltage to ensure good transferability of solid colors may result in undesirable results. In this embodiment, adjustments are made according to the priority image selected by the priority image selection section 708b.

[0101] If "midtones" is selected in the priority image selection unit 708b, the control unit 30 (adjustment process unit 31d) performs adjustments in "midtone priority mode" and selects adjustment values ​​that optimize the transferability of midtone toner images. Also, if "solid image" is selected in the priority image selection unit 708b, the control unit 30 (adjustment process unit 31d) performs adjustments in "solid image priority mode" and selects adjustment values ​​that optimize the transferability of dense toner images such as solid images. In the following explanation of the process for selecting patches with good transferability, B solid patch 101, Bk solid patch 102, and BkHT patch are assumed to be adjustment patches 101A, 102A, and 103A, respectively.

[0102] The midtone priority mode will now be explained. Figure 16 is a graph illustrating the process of selecting patches with good transferability in the midtone priority mode. Figure 16(a) shows an example of the acquisition results of the average brightness value for each patch number of the BkHT patch 103. Figure 16(b) shows an example of the acquisition results of the average brightness value for each patch number of the Bk solid patch 102. Figure 16(c) shows an example of the acquisition results of the average brightness value for each patch number of the B solid patch 101. In the midtone priority mode, the control unit 30 (adjustment process unit 31d) first narrows down the adjustment values ​​using the BkHT patch 103 (S11). As shown in Figure 16(a), in this embodiment, in S11, the patch numbers are narrowed down to a value (threshold L1) less than or equal to the lowest average brightness value multiplied by a coefficient of 1.2. In the illustrated example, the patch numbers are narrowed down to 1 to 5. Next, the control unit 30 (adjustment process unit 31d) narrows down the adjustment values ​​using the Bk solid patch 102 (S12). As shown in Figure 16(b), in this embodiment, in S12, the patch numbers narrowed down in S11 are narrowed down to those with a value (threshold L2) less than or equal to the lowest average brightness value multiplied by a coefficient of 1.2. In the illustrated example, among the patch numbers 1 to 5 narrowed down in S11, the number is narrowed down to patch numbers 3 to 5. Finally, the control unit 30 (adjustment process unit 31d) narrows down the adjustment value by the B solid patch 101 (S13). As shown in Figure 16(c), in this embodiment, in S13, the patch number with the lowest average brightness value is selected among the patch numbers narrowed down in S11 and S12. In the illustrated example, among the patch numbers 3 to 5 narrowed down in S11 and S12, patch number 5 is selected. Then, the control unit 30 (adjustment process unit 31d) selects this patch number 5 (n A The adjustment value corresponding to ) is the recommended adjustment value (N) for good transferability in midtone priority mode. A ) is decided as (S16).

[0103] The solid color image priority mode will now be explained. Figure 17 is a graph illustrating the process of selecting patches with good transferability in the solid color image priority mode. Figure 17(a) shows an example of the acquisition results of the average brightness value for each patch number of the BkHT patch 103. Figure 17(b) shows an example of the acquisition results of the average brightness value for each patch number of the Bk solid color patch 102. Figure 17(c) shows an example of the acquisition results of the average brightness value for each patch number of the B solid color patch 101. The average brightness values ​​shown in Figures 17(a), (b), and (c) are assumed to be the same as the average brightness values ​​shown in Figures 16(a), (b), and (c). In the solid color image priority mode, the control unit 30 (adjustment process unit 31d) does not narrow down the adjustment values ​​using the BkHT patch 103, but instead narrows down the adjustment values ​​using the Bk solid color patch 102 (S14). As shown in Figure 17(b), in this embodiment, in S14, the patch numbers are narrowed down to those less than or equal to the value obtained by multiplying the lowest average brightness value by a coefficient of 1.2 (threshold L2). In the illustrated example, the patch numbers are narrowed down to 3 to 8. Next, the control unit 30 (adjustment process unit 31d) narrows down the adjustment value using the B solid patch 101 (S15). As shown in Figure 17(c), in this embodiment, in S15, the patch number with the lowest average brightness value is selected from among the patch numbers narrowed down in S14. In the illustrated example, patch number 8 is selected from among patch numbers 3 to 8 narrowed down in S14. Then, the control unit 30 (adjustment process unit 31d) selects this patch number 8 (n A The adjustment value corresponding to ) is the recommended adjustment value (N) for good transferability in solid image priority mode. A ) is decided as (S16).

[0104] Thus, the adjustment value N selected differs between the midtone priority mode and the solid image priority mode. A The results are different. This is due to the difference between whether or not filtering was performed using BkHT patch 103, and the midtone priority mode with filtering enabled is able to select adjustment values ​​with lower (smaller absolute) secondary transfer voltages.

[0105] In addition, the coefficient values ​​are not limited to the above values, nor are the narrowing methods limited to the above methods, regardless of whether the narrowing is done using the BkHT patch 103 or the Bk solid patch 102. For example, methods such as pre-storing luminance tolerance values ​​in the ROM 32, or extracting a certain number of patch numbers in order of lowest average luminance values ​​are possible. Furthermore, in this embodiment, the transferability was determined using the average luminance value, but it may also be done using the variance value. Transferability may also be determined using both the average luminance value and the variance value. The variance value is effective in detecting density unevenness within a patch. For example, in narrowing down the adjustment value using a solid patch, in addition to narrowing down using the average luminance value (such as extracting a certain number of patch numbers in order of lowest average luminance value), narrowing down using the variance value (such as selecting the patch number with the smallest variance value) can be performed. Also, depending on the conditions of the image forming apparatus 1 and recording material S during adjustment, there may be no difference in the adjustment results depending on the preferred image.

[0106] The control unit 30 (adjustment process unit 31d) then selects the adjustment value N as described above. A The adjustment value N is displayed on the display unit 70a of the operation unit 70, on the adjustment value display unit 707 of the secondary transfer voltage adjustment screen 706 as shown in Figure 11 (S17). The operator determines whether the displayed content of the secondary transfer voltage adjustment screen 706 is correct and adjusts the displayed adjustment value N A If you do not want to change it, operate the confirmation unit 710 (OK button 710a or apply button 710b). Meanwhile, the operator sets the displayed adjustment value N AIf you wish to change the value, you input it into the adjustment value display unit 707 by operating the numeric keypad (not shown) on the operation unit 70, and then operate the confirmation unit 710 (OK button 710a or apply button 710b). If the adjustment value has been changed, the control unit 30 (adjustment process unit 31d) stores the adjustment value entered by the operator in the RAM 33 (or secondary transfer voltage storage unit / calculation unit 31f) (S18). The operator can then visually check the outputted chart to determine whether the display content of the secondary transfer voltage adjustment screen 706 is correct. On the other hand, if the adjustment value has not been changed and the confirmation unit 710 has been operated, the control unit 30 (adjustment process unit 31d) stores the adjustment value determined by the control unit 30 in the RAM 33 (or secondary transfer voltage storage unit / calculation unit 31f) as is (S18). This completes the adjustment mode.

[0107] Thus, in this embodiment, the image forming apparatus 1 includes an image carrier 44b that carries a toner image, a transfer means 45b that transfers the toner image from the image carrier 44b to the recording material S in the transfer unit N2, an application means 76 that applies a transfer voltage to the transfer means 45b, an execution unit (in this embodiment, the adjustment process unit 31d of the control unit 30) that controls the execution of an output mode to output a chart 100 formed by transferring multiple test images onto the recording material S with different transfer voltages, an acquisition unit 3 that acquires density information regarding the density of the test image on the recording material, a setting unit (in this embodiment, the adjustment process unit 31d of the control unit 30 or the secondary transfer voltage storage unit / calculation unit 31f) that sets the transfer voltage based on the density information acquired by the acquisition unit 3, and an input unit (this In the embodiment, the system includes an operation unit 70), and the execution unit 31d is capable of controlling the transfer of a plurality of first test images having a density of a first density on the image carrier to the recording material S, and is also capable of controlling the transfer of a plurality of second test images having a density of a second density higher than the first density on the image carrier to the recording material S. The setting unit 30 can set a first transfer voltage using the density information of at least the first test image among the first and second test images (midtone priority) or set a second transfer voltage using the density information of at least the second test image among the first and second test images without using the density information of the first test image (solid image priority).

[0108] In this embodiment, the setting unit 30 sets the first transfer voltage using the density information of the first and second test images. More specifically, in this embodiment, the setting unit 30 sets the first transfer voltage based on information regarding the transfer voltage when a first test image whose density information satisfies predetermined conditions is transferred to the recording material S from among a plurality of first test images, and when a second test image whose density information satisfies predetermined conditions is transferred to the recording material S from among a plurality of second test images. In this embodiment, the absolute value of the second transfer voltage is greater than or equal to the absolute value of the first transfer voltage. In addition, in this embodiment, the setting unit 30 sets the second transfer voltage based on information regarding the transfer voltage when a second test image whose density information satisfies predetermined conditions is transferred to the recording material from among a plurality of second test images. In addition, in this embodiment, the execution unit 31d controls the system to output a chart 100 formed by transferring the first and second test images to the recording material S. Furthermore, the execution unit 31d may be controllable to execute a first output mode in which only the first test image of the two test images is transferred to the recording material S and forms a chart 100, or to execute a second output mode in which only the second test image of the two test images is transferred to the recording material S and forms a chart 100, depending on the instruction information input by the input unit 70. In this embodiment, the first test image is a halftone image, and the second test image is a solid color image. In this embodiment, the acquisition unit 3 acquires density information of the test image on the recording material when the recording material S on which the chart is formed is discharged from the image forming apparatus 1.

[0109] As described above, according to this embodiment, in adjustment mode, the user-selected priority image (midtone priority, solid color priority) can be reflected in the adjustment value. Therefore, according to this embodiment, the secondary transfer voltage can be appropriately adjusted for the image that the user prioritizes.

[0110] [Example 2] Next, other embodiments of the present invention will be described. The basic configuration and operation of the image forming apparatus in this embodiment are the same as those of the image forming apparatus in Embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus in Embodiment 1 are denoted by the same reference numerals as in Embodiment 1, and detailed descriptions are omitted.

[0111] The operation of the adjustment mode in this embodiment will now be described. Figure 18 is a flowchart showing an overview of the procedure for the adjustment mode in this embodiment. In Figure 18, the same steps as in the adjustment mode in Embodiment 1 shown in Figure 8 are given the same step numbers as in Figure 8, and detailed explanations are omitted as appropriate. In Embodiment 1, there were two levels of preferred image selection, but in this embodiment, there are three levels of preferred image selection.

[0112] Figure 19 is a schematic diagram of the secondary transfer voltage adjustment screen 706 displayed on the display unit 70a of the operation unit 70 under the control of the control unit 30 (adjustment process unit 31d) in S1 in this embodiment. In this embodiment, the secondary transfer voltage adjustment screen 706 differs from Embodiment 1 in that the priority image selection unit 708c, which selects the density of the image to be optimized in the adjustment mode, is selected. In this embodiment, the priority image selection unit 708c can select the priority image from three options: "low density midtone," "high density midtone," and "solid image." The content entered in the determination of adjustment conditions (S1) is stored in RAM 33 and reflected in subsequent processing.

[0113] The low-density midtone priority mode will now be explained. Figure 20 is a graph illustrating the process of selecting patches with good transferability in the low-density midtone priority mode. Figure 20(a) shows an example of the acquisition results of the average brightness value for each patch number of the BkHT patch 103. Figure 20(b) shows an example of the acquisition results of the average brightness value for each patch number of the Bk beta patch 102. Figure 20(c) shows an example of the acquisition results of the average brightness value for each patch number of the B beta patch 101. In the low-density midtone priority mode, the control unit 30 (adjustment process unit 31d) first narrows down the adjustment values ​​using the BkHT patch 103 (S21). As shown in Figure 20(a), in this embodiment, in S21, the patch numbers are narrowed down to a value (threshold L3) less than or equal to the lowest average brightness value multiplied by a coefficient of 1.1. In the illustrated example, the patch numbers are narrowed down to 1 to 4. Next, the control unit 30 (adjustment process unit 31d) narrows down the adjustment values ​​using the Bk solid patch 102 (S22). As shown in Figure 20(b), in this embodiment, in S22, among the patch numbers narrowed down in S21, the control unit narrows down to patch numbers less than or equal to the value obtained by multiplying the lowest average brightness value by a coefficient of 1.2 (threshold L4). In the illustrated example, among the patch numbers 1 to 4 narrowed down in S21, the control unit narrows down to patch numbers 3 to 4. Finally, the control unit 30 (adjustment process unit 31d) narrows down the adjustment values ​​using the B solid patch 101 (S23). As shown in Figure 20(c), in this embodiment, in S23, among the patch numbers narrowed down in S21 and S22, the control unit selects the patch number with the lowest average brightness value. In the illustrated example, among the patch numbers 3 to 4 narrowed down in S21 and S22, the control unit selects patch number 4. Then, the control unit 30 (adjustment process unit 31d) selects this patch number 4 (n A The adjustment value corresponding to ) is the recommended adjustment value (N) for good transferability in low concentration intermediate-priority mode. A ) is decided as (S16).

[0114] The high-density midtone priority mode will now be explained. Figure 21 is a graph illustrating the process of selecting patches with good transferability in the high-density midtone priority mode. Figure 21(a) shows an example of the acquisition results of the average brightness value for each patch number of the BkHT patch 103. Figure 21(b) shows an example of the acquisition results of the average brightness value for each patch number of the Bk beta patch 102. Figure 21(c) shows an example of the acquisition results of the average brightness value for each patch number of the B beta patch 101. The average brightness values ​​shown in Figures 21(a), (b), and (c) are assumed to be the same as the average brightness values ​​shown in Figures 20(a), (b), and (c). Even in the high-density midtone priority mode, the control unit 30 (adjustment process unit 31d) first narrows down the adjustment values ​​using the BkHT patch 103 (S24). As shown in Figure 21(a), in this embodiment, in S24, the patch numbers are narrowed down to those with a value (threshold L3') or less obtained by multiplying the lowest average brightness value by a coefficient of 1.2. Thus, the coefficient used for narrowing down the BkHT patch 103 in the high-density midtone priority mode is different from the coefficient used for narrowing down the BkHT patch 103 in the low-density midtone priority mode. This coefficient in the high-density midtone priority mode is larger than this coefficient in the low-density midtone priority mode. In other words, the narrowing down of the adjustment value by the BkHT patch 103 in the high-density midtone priority mode is less gradual than the narrowing down by the BkHT patch 103 in the low-density midtone priority mode. In the illustrated example, the patch numbers are narrowed down to 1 to 5. Next, the control unit 30 (adjustment process unit 31d) narrows down the adjustment value by the Bk solid patch 102 (S25). As shown in Figure 21(b), in this embodiment, in S25, the patch numbers are narrowed down to those less than or equal to the value obtained by multiplying the lowest average luminance value by a coefficient of 1.2 (threshold L4) among the patch numbers narrowed down in S24. In the illustrated example, the patch numbers are narrowed down to 3 to 5 among the patch numbers 1 to 5 narrowed down in S24. Finally, the control unit 30 (adjustment process unit 31d) narrows down the adjustment values ​​using the B solid patch 101 (S26). As shown in Figure 21(c), in this embodiment, in S26, the patch number with the lowest average brightness value is selected from among the patch numbers narrowed down in S24 and S25.In the illustrated example, patch number 5 is selected from patch numbers 3 to 5 narrowed down in S24 and S25. Then, the control unit 30 (adjustment process unit 31d) selects this patch number 5 (n. A The adjustment value corresponding to ) is the recommended adjustment value (N) for good transferability in high-concentration intermediate-priority mode. A ) is decided as (S16).

[0115] The solid color image priority mode will now be explained. Figure 22 is a graph illustrating the process of selecting patches with good transferability in the solid color image priority mode. Figure 22(a) shows an example of the acquisition results of the average brightness value for each patch number of the BkHT patch 103. Figure 22(b) shows an example of the acquisition results of the average brightness value for each patch number of the Bk solid color patch 102. Figure 22(c) shows an example of the acquisition results of the average brightness value for each patch number of the B solid color patch 101. The average brightness values ​​shown in Figures 22(a), (b), and (c) are assumed to be the same as the average brightness values ​​shown in Figures 20(a), (b), and (c). In the solid color image priority mode, the control unit 30 (adjustment process unit 31d) does not narrow down the adjustment values ​​using the BkHT patch 103, but instead narrows down the adjustment values ​​using the Bk solid color patch 102 (S27). As shown in Figure 22(b), in this embodiment, in S27, the patch numbers are narrowed down to those less than or equal to the value obtained by multiplying the lowest average brightness value by a coefficient of 1.2 (threshold L4). In the illustrated example, the patch numbers are narrowed down to 3 to 8. Next, the control unit 30 (adjustment process unit 31d) narrows down the adjustment value by the B solid patch 101 (S28). As shown in Figure 22(c), in this embodiment, in S28, the patch number with the lowest average brightness value is selected from the patch numbers narrowed down in S27. In the illustrated example, patch number 8 is selected from the patch numbers 3 to 8 narrowed down in S27. Then, the control unit 30 (adjustment process unit 31d) selects this patch number 8 (n A The adjustment value corresponding to ) is the recommended adjustment value (N) for good transferability in solid image priority mode. A ) is decided as (S16).

[0116] Thus, the selected adjustment value N differs depending on whether you choose the low-density midtone priority mode, the high-density midtone priority mode, or the solid image priority mode. A These differ. This is due to the difference in whether or not filtering was performed using BkHT patch 103, or the degree of filtering, and the mode that prioritizes low concentrations is able to select adjustment values ​​with lower (smaller absolute) secondary transfer voltages.

[0117] Furthermore, in the filtering process using either the BkHT patch 103 or the Bk solid patch 102, the coefficient values ​​are not limited to the above values, nor are the filtering methods limited to the above methods. For example, methods such as pre-storing luminance tolerance values ​​in the ROM 32, or extracting a certain number of patch numbers in order of lowest average luminance value, are possible. Also, the adjustment value between the low-density midtone priority mode and the solid image priority mode may be set to the high-density midtone priority mode. In this embodiment, the transferability was determined using the average luminance value, but it may also be done using the variance value. Transferability may also be determined using both the average luminance value and the variance value. In addition, depending on the conditions of the image forming apparatus 1 and recording material S during adjustment, there may be no difference in the adjustment results depending on the preferred image.

[0118] Thus, in this embodiment, the setting unit 30 can set a first transfer voltage using the density information of at least the first test image among the first and second test images (prioritizing low density midtones), set a second transfer voltage using the density information of at least the second test image among the first and second test images without using the density information of the first test image (prioritizing solid images), or set a third transfer voltage using the density information of at least the first test image among the first and second test images (prioritizing high density midtones). In this embodiment, the setting unit 30 is configured to set a first transfer voltage and a third transfer voltage using density information of a first test image and a second test image. The first transfer voltage is set based on information regarding the transfer voltage when a first test image whose density information satisfies a predetermined first condition is transferred to the recording material S from among a plurality of first test images, and the transfer voltage when a second test image whose density information satisfies a predetermined condition is transferred to the recording material S from among a plurality of second test images. The third transfer voltage is set based on information regarding the transfer voltage when a first test image whose density information satisfies a predetermined second condition different from the first condition is transferred to the recording material S from among a plurality of second test images, and the transfer voltage when a second test image whose density information satisfies a predetermined condition is transferred to the recording material S from among a plurality of second test images. In this embodiment, the absolute value of the third transfer voltage is greater than or equal to the absolute value of the first transfer voltage, and the absolute value of the second transfer voltage is greater than or equal to the absolute value of the third transfer voltage.

[0119] As described above, according to this embodiment, in adjustment mode, the user-selected priority image (low-density midtone priority, high-density midtone priority, solid image priority) can be reflected in the adjustment value. Therefore, according to this embodiment, the secondary transfer voltage can be appropriately adjusted for the image that the user prioritizes.

[0120] [Example 3] Next, other embodiments of the present invention will be described. The basic configuration and operation of the image forming apparatus in this embodiment are the same as those of the image forming apparatus in Embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus in Embodiment 1 are denoted by the same reference numerals as in Embodiment 1, and detailed descriptions are omitted.

[0121] The operation of the adjustment mode in this embodiment will now be described. Figure 23 is a flowchart showing an overview of the procedure for the adjustment mode in this embodiment. In Figure 23, the same steps as in the adjustment mode in Embodiment 1 shown in Figure 8 are given the same step numbers as in Figure 8, and detailed explanations are omitted as appropriate. In Embodiment 1, the chart formed in the adjustment mode was the same regardless of the preferred image, but in this embodiment, the chart formed in the adjustment mode is changed according to the preferred image.

[0122] Figure 24 is a schematic diagram of the secondary transfer voltage adjustment screen 706 displayed on the display unit 70a of the operation unit 70 under the control of the control unit 30 (adjustment process unit 31d) in S1 in this embodiment. In this embodiment, the secondary transfer voltage adjustment screen 706 differs from Embodiment 1 in that the priority image selection unit 708d, which selects the density of the image to be optimized in the adjustment mode, is selected. In this embodiment, the priority image selection unit 708d can select the priority image from two options: "low density" and "high density". The content entered in the determination of adjustment conditions (S1) is stored in RAM 33 and reflected in subsequent processing.

[0123] In this embodiment, after ATVC control (S3), the control unit 30 (adjustment process unit 31d) first refers to the input result from the priority image selection unit 708d (S31). Specifically in this embodiment, in S31, it is determined whether or not the low density priority mode is selected. If "low density" is selected in the priority image selection unit 708b, the control unit 30 (adjustment process unit 31d) performs adjustment as the "low density priority mode," and if "high density" is selected, it performs adjustment as the "high density priority mode." In this embodiment, the control unit 30 (adjustment process unit 31d) changes the density of the BkHT patch 103 according to the priority image (S32, S33). In other words, in this embodiment, in the "low density priority mode," the control unit 30 (adjustment process unit 31d) sets the density of the BkHT patch 103 to a light midtone (S32). In this embodiment, when the output of the exposure device 42 during non-image formation is 0 and the output of the exposure device 42 during image formation of the Bk solid patch 102 is 255, the output of the exposure device 42 during image formation of the BkHT patch 103 in "low density priority mode" is set to 96. On the other hand, in "high density priority mode", the control unit 30 (adjustment process unit 31d) sets the density of the BkHT patch 103 to a dark midtone (S33). In this embodiment, when the output of the exposure device 42 during non-image formation is 0 and the output of the exposure device 42 during image formation of the Bk solid patch 102 is 255, the output of the exposure device 42 during image formation of the BkHT patch 103 in "high density priority mode" is set to 192. As described above, the control unit 30 (adjustment process unit 31d) sets the density of the BkHT patch 103 according to the priority image and outputs a chart (S4). The arrangement of patches on the chart is the same as in Embodiment 1. Also, the processing from S5 to S9 is the same as in Embodiment 1.

[0124] After S9, the control unit 30 (adjustment process unit 31d) proceeds to select a patch with good transferability. In this embodiment, the conditions for narrowing down the adjustment value in the BkHT patch 103 are not changed according to the preferred image. That is, confirmation of transferability with the BkHT patch 103 (S34), confirmation of transferability with the Bk solid patch (S35), confirmation of transferability with the B solid patch (S36), and adjustment value N AThe determination (S16) is performed similarly regardless of the preferred image. In this embodiment, since the density of the BkHT patch 103 itself differs depending on the preferred image, differences in the filtering results occur even without changing the filtering conditions.

[0125] An example of adjustment in low-concentration priority mode will be described. Figure 25 is a graph illustrating the process of selecting patches with good transferability in low-concentration priority mode. Figure 25(a) shows an example of the acquisition results of the average brightness value for each patch number of the BkHT patch 103. Figure 25(b) shows an example of the acquisition results of the average brightness value for each patch number of the Bk beta patch 102. Figure 25(c) shows an example of the acquisition results of the average brightness value for each patch number of the B beta patch 101. The control unit 30 (adjustment process unit 31d) first narrows down the adjustment values ​​using the BkHT patch 103 (S34). As shown in Figure 25(a), in this embodiment, in S34, the patch numbers are narrowed down to a value (threshold L5) that is less than or equal to the lowest average brightness value multiplied by a coefficient of 1.2. In the illustrated example, the patch numbers are narrowed down to 1 to 4. Next, the control unit 30 (adjustment process unit 31d) narrows down the adjustment values ​​using the Bk beta patch 102 (S35). As shown in Figure 25(b), in this embodiment, in S35, the patch numbers narrowed down in S34 are narrowed down to those with a value (threshold L6) less than or equal to the lowest average brightness value multiplied by a coefficient of 1.2. In the illustrated example, among the patch numbers 1 to 4 narrowed down in S34, the number is narrowed down to patch numbers 3 to 4. Finally, the control unit 30 (adjustment process unit 31d) narrows down the adjustment value by the B solid patch 101 (S36). As shown in Figure 25(c), in this embodiment, in S36, the patch number with the lowest average brightness value is selected among the patch numbers narrowed down in S34 and S35. In the illustrated example, among the patch numbers 3 to 4 narrowed down in S34 and S35, patch number 4 is selected. Then, the control unit 30 (adjustment process unit 31d) selects this patch number 4 (n A The adjustment value corresponding to ) is the recommended adjustment value (N) for good transferability in low-concentration priority mode. A ) is decided as (S16).

[0126] An example of adjustment in high-density priority mode will be described. Figure 26 is a graph illustrating the process of selecting patches with good transferability in high-density priority mode. Figure 26(a) shows an example of the acquisition results of the average brightness value for each patch number of the BkHT patch 103. Figure 26(b) shows an example of the acquisition results of the average brightness value for each patch number of the Bk beta patch 102. Figure 26(c) shows an example of the acquisition results of the average brightness value for each patch number of the B beta patch 101. The control unit 30 (adjustment process unit 31d) first narrows down the adjustment values ​​using the BkHT patch 103 (S34). Compared with the low-density priority mode shown in Figure 25(a), the average brightness value of the BkHT patch 103 in high-density priority mode shown in Figure 26(a) shows that patch numbers with low brightness (good transferability, high density) have shifted to the side with higher voltage. As shown in Figure 26(a), in this embodiment, in S34, the patch numbers are narrowed down to those less than or equal to the value obtained by multiplying the lowest average brightness value by a coefficient of 1.2 (threshold L5'). In the illustrated example, the patch numbers are narrowed down to 1 to 6. Next, the control unit 30 (adjustment process unit 31d) narrows down the adjustment value using the Bk solid patch 102 (S35). As shown in Figure 26(b), in this embodiment, in S35, the patch numbers are narrowed down to those less than or equal to the value obtained by multiplying the lowest average brightness value by a coefficient of 1.2 (threshold L6) among the patch numbers narrowed down in S34. In the illustrated example, the patch numbers are narrowed down to 3 to 6 among the patch numbers 1 to 6 narrowed down in S34. Finally, the control unit 30 (adjustment process unit 31d) narrows down the adjustment value using the B solid patch 101 (S36). As shown in Figure 26(c), in this embodiment, in S36, the patch number with the lowest average brightness value is selected from among the patch numbers narrowed down in S34 and S35. In the illustrated example, patch number 6 is selected from among patch numbers 3 to 6 narrowed down in S34 and S35. Then, the control unit 30 (adjustment process unit 31d) selects this patch number 6(n A The adjustment value corresponding to ) is the recommended adjustment value (N) for good transferability in high-concentration priority mode. A ) is decided as (S16).

[0127] Thus, the selected adjustment value N differs between the low-concentration priority mode and the high-concentration priority mode. A These differ. This is due to the difference in the concentration of BkHT patch 103 used for adjustment; the mode prioritizing lower concentrations allows for the selection of adjustment values ​​with lower (smaller absolute) secondary transfer voltages.

[0128] The density of the BkHT patch 103 is not limited to the above values; for example, it may be specified directly by the user or changed according to the image actually output by the user. Such changes can be made, for example, from the control unit 70 or external device 200. In this embodiment, the transferability was determined using the average brightness value, but it may also be done using the variance value. The transferability may also be determined using both the average brightness value and the variance value. Furthermore, depending on the conditions of the image forming apparatus 1 and recording material S during adjustment, there may be no difference in the adjustment results depending on the preferred image.

[0129] Thus, in this embodiment, the execution unit 31d can control the transfer of a plurality of third test images to the recording material S, in addition to the first and second test images described above, where the density on the image carrier is higher than the second density. The setting unit 30 sets a first transfer voltage using the density information of the first and third test images (low density priority) and sets a second transfer voltage using the density information of the second and third test images (high density priority). More specifically, in this embodiment, the setting unit 30 sets a first transfer voltage based on information relating to the transfer voltage when a first test image whose density information satisfies predetermined conditions is transferred to the recording material S from among a plurality of first test images, and the transfer voltage when a third test image whose density information satisfies predetermined conditions is transferred to the recording material S from among a plurality of third test images. The setting unit 30 sets a second transfer voltage based on information relating to the transfer voltage when a second test image whose density information satisfies predetermined conditions is transferred to the recording material S from among a plurality of second test images, and the transfer voltage when a third test image whose density information satisfies predetermined conditions is transferred to the recording material S from among a plurality of third test images. In this embodiment, the absolute value of the second transfer voltage is greater than or equal to the absolute value of the first transfer voltage. In this embodiment, the execution unit 31d can be controlled to either execute a first output mode in which only the first and third test images out of the first, second, and third test images are transferred to the recording material S and output a chart 100, or execute a second output mode in which only the second and third test images out of the first, second, and third test images are transferred to the recording material S and output a chart 100, depending on the instruction information input by the input unit 70. In this embodiment, the first and second test images are halftone images, and the third test image is a solid color image.

[0130] As described above, according to this embodiment, in adjustment mode, the user-selected priority image (low density priority, high density priority) can be reflected in the adjustment value. Therefore, according to this embodiment, the secondary transfer voltage can be appropriately adjusted for the image that the user prioritizes.

[0131] [others] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the embodiments described above.

[0132] In the above embodiment, the transfer voltage was adjusted using an adjustment value corresponding to a predetermined adjustment amount, but the adjustment amount may be set directly, for example, on an adjustment screen.

[0133] Furthermore, in the above-described embodiment, the control unit determined the adjustment amount (adjustment value) of the secondary transfer voltage for one selected preferred image in a single adjustment mode. In contrast, the control unit may also determine and store the adjustment amounts (adjustment values) of the secondary transfer voltage for multiple (or all) of the preferred image options in a single adjustment mode. Before or after these multiple adjustment amounts (adjustment values) are determined and stored, the operator can select a preferred image in the same manner as in the above-described embodiment. The control unit can then set the secondary transfer voltage using the adjustment amount (adjustment value) corresponding to the preferred image selected by the operator from among the multiple stored adjustment amounts (adjustment values).

[0134] Furthermore, the operations described in the above embodiment, which are performed on the operation unit of the image forming apparatus, can be performed on an external device. In other words, although the case in which the adjustment mode is executed by an operator via the operation unit 70 of the image forming apparatus 1 has been described, the adjustment mode may also be executed by an external device 200 such as a personal computer. In this case, the same settings as in the above embodiment can be made via a screen displayed on the display unit of the external device 200 by the driver program of the image forming apparatus 1 installed on the external device 200.

[0135] Furthermore, although the above-described embodiment described a configuration in which the secondary transfer voltage is controlled by a constant voltage, the secondary transfer voltage may also be controlled by a constant current. In the above-described embodiment, in the configuration in which the secondary transfer voltage is controlled by a constant voltage, the secondary transfer voltage was adjusted by adjusting the target voltage when the secondary transfer voltage is applied using the adjustment mode. In the case of a configuration in which the secondary transfer voltage is controlled by a constant current, the secondary transfer voltage can be adjusted by adjusting the target current when the secondary transfer voltage is applied using the adjustment mode.

[0136] Furthermore, the current detection result and the voltage detection result may be the average value of multiple sampled values ​​acquired at a predetermined sampling interval at a single detection timing. Also, when the transfer voltage is controlled by a constant voltage, the voltage value may be detected (recognized) from the output instruction value to the power supply, and when the transfer voltage is controlled by a constant current, the current value may be detected (recognized) from the output instruction value to the power supply.

[0137] Furthermore, in the above-described embodiment, the chart was read using inline image sensors (first and second line sensors 91 and 92) in the adjustment mode. This reduces the burden on the operator. However, the present invention is not limited to this embodiment. For example, the operator may set the chart output in the adjustment mode into the image reading unit 80, which acts as an acquisition unit, and read the chart using the image reading unit 80. In this way, the acquisition unit 80 may be configured to receive the recording material S on which the chart has been formed, which has been discharged from the image forming apparatus 1, and to acquire density information of the test image on the recording material. Alternatively, for example, the operator may read the chart output in the adjustment mode using an image reading means prepared separately from the image forming apparatus 1. In this case, the information of the read image, the brightness information (density information) of the read patch, or the information of the adjustment value (adjustment amount) selected by processing these with an external device can be input to the image forming apparatus 1. This information can be input via a network, via a storage medium from the operation unit 70, or directly from the operation unit 70 by the operator using key input or the like. In this case, the control unit 30 of the image forming apparatus 1 can, based on the input image information and brightness information (density information), suggest a recommended adjustment amount for the secondary transfer voltage in the same manner as in the embodiment described above.

[0138] Furthermore, in the above-described embodiment, the image forming apparatus had a printer unit and a sensing unit, each unitized separately, but the present invention is not limited to this embodiment. With such a configuration, for example, the units can be separated, and the functions of the sensing unit can be provided as an extended function of the image forming apparatus. However, the configuration of the printer unit and the configuration of the sensing unit in the above-described embodiment may be arranged and integrated within a single housing, for example.

[0139] Furthermore, the image forming apparatus is not limited to a tandem type image forming apparatus, but may be an image forming apparatus of another type. Also, the image forming apparatus is not limited to an image forming apparatus capable of forming full-color images, but may be an image forming apparatus capable of forming only monochrome (black and white or monocolor) images. For example, the present invention may be applied to the transfer unit in an image forming apparatus configured to form a toner image on a photosensitive drum as an image carrier and transfer it directly to a recording material in a transfer unit. Furthermore, the image forming apparatus may be an image forming apparatus for various purposes, such as a printer, various printing machines, copiers, fax machines, and multifunction devices. [Explanation of Symbols]

[0140] 2 Image forming apparatus 3. Sensing Unit 4 Paper feed section 7 Reversal transport path 8 Discharge section 30 Control Unit 70 Operation section 76 Secondary Transfer Power Supply 80 Image reading unit 91 First line sensor 92 Second line sensor 100 Charts 100L Large Chart (L Chart) 100S Small Chart (S Chart) 101 B Beta Patch 102 Black Beta Patch 103 BkHT Patch N2 Secondary Transfer Section

Claims

1. An image carrier that holds the toner image, A transfer device for transferring a toner image from the image carrier to a recording material, The transfer apparatus includes an application unit for applying voltage, A detection unit that detects density information relating to the density of an image on a recording material onto which an image is transferred by the transfer device, A control unit that, when not forming an image, applies multiple different test voltages to the transfer device to transfer multiple test images onto a recording material, and performs a setting mode operation to set the transfer voltage to be applied to the transfer device during image formation based on the detection result detected by the detection unit of the test images transferred onto the recording material, The reception desk receives instruction information, It has, When the operation of the setting mode is performed to set the transfer voltage in a single-sided mode in which an image is formed on one side of a predetermined recording material, the receiving unit is capable of receiving instruction information that selectively specifies a mode to be executed from among a plurality of modes, including a first setting mode in which the transfer voltage is set so that the transfer voltage set in the setting mode satisfies a first predetermined condition, and a second setting mode in which the transfer voltage is set so that the transfer voltage set in the setting mode satisfies a second predetermined condition different from the first predetermined condition. The test image includes a plurality of first test images having a first density on the recording material and a plurality of second test images having a second density on the recording material, wherein the second density is higher than the first density. The first predetermined condition includes a first condition relating to the plurality of first test images, and the second predetermined condition includes a second condition relating to the plurality of first test images, and the second condition differs from the first condition. An image forming apparatus characterized in that, in the first setting mode, the transfer voltage is set prioritizing the transferability of an image of a first predetermined density, and in the second setting mode, the transfer voltage is set prioritizing the transferability of an image of a second predetermined density higher than the first predetermined density.

2. In cases where the transfer voltage can be set such that the image density after transferring the plurality of first test images is equal to or greater than a first threshold, and the image density after transferring the plurality of second test images is equal to or greater than a second threshold that is higher than the first threshold, When the first setting mode is selected, the transfer voltage is set such that the image density after transferring the plurality of first test images is equal to or greater than the first threshold, and the transfer voltage is set such that the image density after transferring the plurality of second test images is equal to or greater than the second threshold. The image forming apparatus according to claim 1, characterized in that, when the second setting mode is selected, the transfer voltage is set such that the image density after transferring the plurality of second test images is equal to or greater than the second threshold, without using density information relating to the density of the first test image.

3. The image forming apparatus according to claim 1 or 2, characterized in that the transfer voltage set in the second setting mode is equal to or greater than the transfer voltage set in the first setting mode.

4. The image forming apparatus according to any one of claims 1 to 3, characterized in that the first test image is a halftone image and the second test image is a solid image.

Images